diff --git a/pipeline/adapters/animation/html.py b/pipeline/adapters/animation/html.py
index c55fce2..f47117a 100644
--- a/pipeline/adapters/animation/html.py
+++ b/pipeline/adapters/animation/html.py
@@ -89,6 +89,9 @@ def render(self, spec: SceneSpec, timing: List[float], output_path: Path) -> Pat
         array = viz_config.get("array", [])
         target = viz_config.get("target", 0)
 
+        # Resolve theme colors
+        theme = spec.visualization.get_resolved_theme()
+
         # Convert steps to serializable format
         steps_data = [
             {
@@ -111,6 +114,7 @@ def render(self, spec: SceneSpec, timing: List[float], output_path: Path) -> Pat
             target=target,
             steps=steps_data,
             timing=timing,
+            theme=theme,
         )
 
         # Ensure output directory exists
diff --git a/pipeline/schema.py b/pipeline/schema.py
index 550ba0f..cc4996d 100644
--- a/pipeline/schema.py
+++ b/pipeline/schema.py
@@ -4,10 +4,104 @@
 Defines the data models for scene specifications that drive the animation pipeline.
 """
 
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Literal, Optional
 from pydantic import BaseModel, Field
 
 
+# Preset theme definitions
+PRESET_THEMES = {
+    "dark": {
+        "background": "#1a1a2e",
+        "text": "#eee",
+        "title": "#e94560",
+        "target": "#16c79a",
+        "cell_bg": "#0f3460",
+        "cell_border": "#16c79a",
+        "cell_text": "#eee",
+        "pointer_left": "#e94560",
+        "pointer_right": "#00b4d8",
+        "highlight_found": "#16c79a",
+        "highlight_sum": "#f7d716",
+        "message": "#f7d716",
+        "index_label": "#888",
+        "step_indicator": "#666",
+    },
+    "light": {
+        "background": "#f5f5f5",
+        "text": "#333",
+        "title": "#d63384",
+        "target": "#198754",
+        "cell_bg": "#ffffff",
+        "cell_border": "#198754",
+        "cell_text": "#333",
+        "pointer_left": "#d63384",
+        "pointer_right": "#0d6efd",
+        "highlight_found": "#198754",
+        "highlight_sum": "#ffc107",
+        "message": "#fd7e14",
+        "index_label": "#6c757d",
+        "step_indicator": "#adb5bd",
+    },
+    "neetcode": {
+        "background": "#0a0a0f",
+        "text": "#e5e5e5",
+        "title": "#ff6b6b",
+        "target": "#51cf66",
+        "cell_bg": "#1a1a2e",
+        "cell_border": "#4dabf7",
+        "cell_text": "#e5e5e5",
+        "pointer_left": "#ff6b6b",
+        "pointer_right": "#4dabf7",
+        "highlight_found": "#51cf66",
+        "highlight_sum": "#ffd43b",
+        "message": "#ffd43b",
+        "index_label": "#868e96",
+        "step_indicator": "#495057",
+    },
+}
+
+
+class ThemeColors(BaseModel):
+    """Custom color overrides for theming.
+
+    All colors are optional. Unspecified colors fall back to the base preset.
+    """
+    background: Optional[str] = None
+    text: Optional[str] = None
+    title: Optional[str] = None
+    target: Optional[str] = None
+    cell_bg: Optional[str] = None
+    cell_border: Optional[str] = None
+    cell_text: Optional[str] = None
+    pointer_left: Optional[str] = None
+    pointer_right: Optional[str] = None
+    highlight_found: Optional[str] = None
+    highlight_sum: Optional[str] = None
+    message: Optional[str] = None
+    index_label: Optional[str] = None
+    step_indicator: Optional[str] = None
+
+
+class ThemeConfig(BaseModel):
+    """Theme configuration for visualization colors.
+
+    Attributes:
+        preset: Base preset theme ("dark", "light", "neetcode")
+        colors: Custom color overrides
+    """
+    preset: Literal["dark", "light", "neetcode"] = "dark"
+    colors: Optional[ThemeColors] = None
+
+    def resolve_colors(self) -> Dict[str, str]:
+        """Resolve final colors by merging preset with overrides."""
+        base = PRESET_THEMES[self.preset].copy()
+        if self.colors:
+            for key, value in self.colors.model_dump().items():
+                if value is not None:
+                    base[key] = value
+        return base
+
+
 class StepState(BaseModel):
     """Visualization state for a single step.
 
@@ -42,9 +136,15 @@ class VisualizationConfig(BaseModel):
     Attributes:
         type: Type of visualization (e.g., "array_pointers")
         config: Type-specific configuration dictionary
+        theme: Optional theme configuration
     """
     type: str
     config: Dict[str, Any] = Field(default_factory=dict)
+    theme: ThemeConfig = Field(default_factory=ThemeConfig)
+
+    def get_resolved_theme(self) -> Dict[str, str]:
+        """Get fully resolved theme colors."""
+        return self.theme.resolve_colors()
 
 
 class SceneSpec(BaseModel):
diff --git a/scenes/two_pointers/scene.json b/scenes/two_pointers/scene.json
index fbb2116..76401e9 100644
--- a/scenes/two_pointers/scene.json
+++ b/scenes/two_pointers/scene.json
@@ -4,7 +4,8 @@
   "description": "Two pointer technique on sorted array",
   "visualization": {
     "type": "array_pointers",
-    "config": {"array": [2, 7, 11, 15], "target": 9, "theme": "dark"}
+    "config": {"array": [2, 7, 11, 15], "target": 9},
+    "theme": {"preset": "dark"}
   },
   "steps": [
     {"id": "init", "narration": "The two pointer approach starts with pointers at both ends. Left at two, right at fifteen.", "state": {"left": 0, "right": 3, "highlight": null, "message": "Initialize: L=0, R=3"}},
diff --git a/templates/array_animation.html b/templates/array_animation.html
index 736ab1a..f79d4c6 100644
--- a/templates/array_animation.html
+++ b/templates/array_animation.html
@@ -5,6 +5,23 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>{{ title }}</title>
     <style>
+        :root {
+            --bg: {{ theme.background }};
+            --text: {{ theme.text }};
+            --title: {{ theme.title }};
+            --target: {{ theme.target }};
+            --cell-bg: {{ theme.cell_bg }};
+            --cell-border: {{ theme.cell_border }};
+            --cell-text: {{ theme.cell_text }};
+            --pointer-left: {{ theme.pointer_left }};
+            --pointer-right: {{ theme.pointer_right }};
+            --highlight-found: {{ theme.highlight_found }};
+            --highlight-sum: {{ theme.highlight_sum }};
+            --message: {{ theme.message }};
+            --index-label: {{ theme.index_label }};
+            --step-indicator: {{ theme.step_indicator }};
+        }
+
         * {
             margin: 0;
             padding: 0;
@@ -12,8 +29,8 @@
         }
 
         body {
-            background: #1a1a2e;
-            color: #eee;
+            background: var(--bg);
+            color: var(--text);
             font-family: 'SF Mono', 'Monaco', 'Inconsolata', 'Fira Code', monospace;
             min-height: 100vh;
             display: flex;
@@ -35,13 +52,13 @@
         .title {
             font-size: 28px;
             font-weight: 600;
-            color: #e94560;
+            color: var(--title);
             text-align: center;
         }
 
         .target-display {
             font-size: 20px;
-            color: #16c79a;
+            color: var(--target);
             text-align: center;
         }
 
@@ -62,47 +79,48 @@
             justify-content: center;
             font-size: 28px;
             font-weight: 600;
-            background: #0f3460;
-            border: 3px solid #16c79a;
+            background: var(--cell-bg);
+            border: 3px solid var(--cell-border);
             border-radius: 12px;
             position: relative;
             transition: all 0.3s ease;
+            color: var(--cell-text);
         }
 
         .array-cell.highlight-left {
-            background: #e94560;
-            border-color: #e94560;
+            background: var(--pointer-left);
+            border-color: var(--pointer-left);
             transform: scale(1.1);
         }
 
         .array-cell.highlight-right {
-            background: #00b4d8;
-            border-color: #00b4d8;
+            background: var(--pointer-right);
+            border-color: var(--pointer-right);
             transform: scale(1.1);
         }
 
         .array-cell.highlight-both {
-            background: linear-gradient(135deg, #e94560 50%, #00b4d8 50%);
-            border-color: #f7d716;
+            background: linear-gradient(135deg, var(--pointer-left) 50%, var(--pointer-right) 50%);
+            border-color: var(--highlight-sum);
             transform: scale(1.15);
         }
 
         .array-cell.highlight-sum {
-            box-shadow: 0 0 20px rgba(247, 215, 22, 0.6);
+            box-shadow: 0 0 20px color-mix(in srgb, var(--highlight-sum) 60%, transparent);
         }
 
         .array-cell.found {
-            background: #16c79a;
-            border-color: #16c79a;
+            background: var(--highlight-found);
+            border-color: var(--highlight-found);
             transform: scale(1.2);
-            box-shadow: 0 0 30px rgba(22, 199, 154, 0.8);
+            box-shadow: 0 0 30px color-mix(in srgb, var(--highlight-found) 80%, transparent);
         }
 
         .index-label {
             position: absolute;
             bottom: -28px;
             font-size: 14px;
-            color: #888;
+            color: var(--index-label);
         }
 
         .pointer {
@@ -117,12 +135,12 @@
         }
 
         .pointer.left-pointer {
-            background: #e94560;
+            background: var(--pointer-left);
             color: white;
         }
 
         .pointer.right-pointer {
-            background: #00b4d8;
+            background: var(--pointer-right);
             color: white;
         }
 
@@ -132,7 +150,7 @@
 
         .message-display {
             font-size: 24px;
-            color: #f7d716;
+            color: var(--message);
             text-align: center;
             min-height: 36px;
             transition: opacity 0.3s ease;
@@ -140,7 +158,7 @@
 
         .step-indicator {
             font-size: 14px;
-            color: #666;
+            color: var(--step-indicator);
         }
 
         /* Animation keyframes for pointer movement */
diff --git a/tests/fixtures/sample_scene.json b/tests/fixtures/sample_scene.json
index 59983bb..d8ada91 100644
--- a/tests/fixtures/sample_scene.json
+++ b/tests/fixtures/sample_scene.json
@@ -6,9 +6,9 @@
     "type": "array_pointers",
     "config": {
       "array": [2, 7, 11, 15],
-      "target": 9,
-      "theme": "dark"
-    }
+      "target": 9
+    },
+    "theme": {"preset": "dark"}
   },
   "steps": [
     {
diff --git a/tests/test_schema.py b/tests/test_schema.py
index bbc916d..c895ca8 100644
--- a/tests/test_schema.py
+++ b/tests/test_schema.py
@@ -8,7 +8,15 @@
 import pytest
 from pydantic import ValidationError
 
-from pipeline.schema import SceneSpec, Step, StepState, VisualizationConfig
+from pipeline.schema import (
+    PRESET_THEMES,
+    SceneSpec,
+    Step,
+    StepState,
+    ThemeColors,
+    ThemeConfig,
+    VisualizationConfig,
+)
 
 
 class TestStepState:
@@ -101,6 +109,57 @@ def test_with_config(self):
         assert viz.config["array"] == [1, 2, 3]
         assert viz.config["target"] == 5
 
+    def test_theme_defaults_to_dark(self):
+        """Theme should default to dark preset."""
+        viz = VisualizationConfig(type="array_pointers")
+        assert viz.theme.preset == "dark"
+
+
+class TestThemeConfig:
+    """Tests for ThemeConfig model."""
+
+    def test_default_preset(self):
+        """ThemeConfig should default to dark preset."""
+        theme = ThemeConfig()
+        assert theme.preset == "dark"
+
+    def test_resolve_colors_dark(self):
+        """Dark preset should resolve to expected colors."""
+        theme = ThemeConfig(preset="dark")
+        colors = theme.resolve_colors()
+        assert colors["background"] == "#1a1a2e"
+        assert colors["pointer_left"] == "#e94560"
+
+    def test_resolve_colors_light(self):
+        """Light preset should resolve to expected colors."""
+        theme = ThemeConfig(preset="light")
+        colors = theme.resolve_colors()
+        assert colors["background"] == "#f5f5f5"
+        assert colors["text"] == "#333"
+
+    def test_resolve_colors_neetcode(self):
+        """Neetcode preset should resolve to expected colors."""
+        theme = ThemeConfig(preset="neetcode")
+        colors = theme.resolve_colors()
+        assert colors["background"] == "#0a0a0f"
+
+    def test_color_overrides(self):
+        """Custom colors should override preset values."""
+        theme = ThemeConfig(
+            preset="dark",
+            colors=ThemeColors(background="#000000", title="#ff0000")
+        )
+        colors = theme.resolve_colors()
+        assert colors["background"] == "#000000"
+        assert colors["title"] == "#ff0000"
+        # Non-overridden values should use preset
+        assert colors["text"] == "#eee"
+
+    def test_invalid_preset_rejected(self):
+        """Invalid preset should raise ValidationError."""
+        with pytest.raises(ValidationError):
+            ThemeConfig(preset="invalid_theme")
+
 
 class TestSceneSpec:
     """Tests for SceneSpec model."""
@@ -195,7 +254,7 @@ def test_sample_scene_visualization(self, sample_scene_data: dict):
         assert spec.visualization.type == "array_pointers"
         assert spec.visualization.config["array"] == [2, 7, 11, 15]
         assert spec.visualization.config["target"] == 9
-        assert spec.visualization.config["theme"] == "dark"
+        assert spec.visualization.theme.preset == "dark"
 
     def test_sample_scene_steps(self, sample_scene_data: dict):
         """Sample scene should have expected steps."""