refactor: enhance to_pptx_rgb_color function to support PptxRGBColor type

Author: ya7010

src/tppt/pptx/converter.py

@@ -97,18 +97,18 @@ def to_tppt_length(length: PptxLength | None) -> Length | None:
 
 @overload
 def to_pptx_rgb_color(
-    color: Color | LiteralColor,
+    color: Color | LiteralColor | PptxRGBColor,
 ) -> tuple[PptxRGBColor, int | None]: ...
 
 
 @overload
 def to_pptx_rgb_color(
-    color: Color | LiteralColor | None,
+    color: Color | LiteralColor | PptxRGBColor | None,
 ) -> tuple[PptxRGBColor, int | None] | None: ...
 
 
 def to_pptx_rgb_color(
-    color: Color | LiteralColor | None,
+    color: Color | LiteralColor | PptxRGBColor | None,
 ) -> (
     tuple[
         PptxRGBColor,

src/tppt/pptx/dml/color.py

@@ -100,13 +100,16 @@ def rgb(self) -> Color:
         solid_fill = cast(
             _Element, self._pptx._xFill.solidFill.get_or_change_to_srgbClr()
         )
-        alpha = solid_fill.find("a:alpha", None)
-        if alpha is not None:
+
+        if alpha := solid_fill.find("a:alpha", namespace):
             alpha = alpha.attrib["val"]
+        else:
+            alpha = None
+
         return to_tppt_rgb_color(cast(PptxRGBColor, self._pptx.rgb), alpha=alpha)
 
     @rgb.setter
-    def rgb(self, color: Color | LiteralColor):
+    def rgb(self, color: Color | LiteralColor | PptxRGBColor):
         pptx_color, alpha = to_pptx_rgb_color(color)
         self._pptx.rgb = pptx_color
         srgbClr = cast(_Element, cast(_SRgbColor, self._pptx._color)._srgbClr)