From 001971b98155ecbf6035f90eecfcb6af4b8a6c47 Mon Sep 17 00:00:00 2001
From: Romain Menke <romainmenke@gmail.com>
Date: Fri, 31 Jul 2026 17:09:02 +0200
Subject: [PATCH 1/4] [css-color-4] set chroma to 0 when converting powerless
 hue to missing

---
 css-color-4/Overview.bs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs
index b1560c8779c..577d3b87c92 100644
--- a/css-color-4/Overview.bs
+++ b/css-color-4/Overview.bs
@@ -1293,6 +1293,11 @@ will have a [=powerless=] hue component.
 	have an <em>extremely small</em> chroma rather than precisely ''0%'';
 	as a result, the hue component is [=powerless=].
 
+	When changing a powerless hue component to a [=missing component=],
+	the chroma (or other measure of colorfulness, such as saturation in ''hsl'') is set to zero
+	to avoid amplifying floating-point noise.
+	In the case of ''hwb'' set ''b'' to ''100 - w'' or if either ''b'' or ''w'' is missing set the other component to ''100''.
+
 <h3 id=parse-color>
 Parsing a <<color>> Value</h3>
 

From d6a935035765b50732a25b2497746de125fb4884 Mon Sep 17 00:00:00 2001
From: Romain Menke <11521496+romainmenke@users.noreply.github.com>
Date: Fri, 31 Jul 2026 17:49:04 +0200
Subject: [PATCH 2/4] Update css-color-4/Overview.bs

Co-authored-by: Chris Lilley <chris@w3.org>
---
 css-color-4/Overview.bs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs
index 577d3b87c92..311208a3cb7 100644
--- a/css-color-4/Overview.bs
+++ b/css-color-4/Overview.bs
@@ -1294,7 +1294,7 @@ will have a [=powerless=] hue component.
 	as a result, the hue component is [=powerless=].
 
 	When changing a powerless hue component to a [=missing component=],
-	the chroma (or other measure of colorfulness, such as saturation in ''hsl'') is set to zero
+	the chroma (or other measure of colorfulness, such as saturation in ''hsl''; see [=analogous components=]) is set to zero
 	to avoid amplifying floating-point noise.
 	In the case of ''hwb'' set ''b'' to ''100 - w'' or if either ''b'' or ''w'' is missing set the other component to ''100''.
 

From 5e8fb4d12aea11c6e8db398da78fda05e827d29e Mon Sep 17 00:00:00 2001
From: Romain Menke <romainmenke@gmail.com>
Date: Sun, 2 Aug 2026 11:07:50 +0200
Subject: [PATCH 3/4] describe hwb in pseudo code

---
 css-color-4/Overview.bs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs
index 311208a3cb7..69adb077699 100644
--- a/css-color-4/Overview.bs
+++ b/css-color-4/Overview.bs
@@ -1296,7 +1296,16 @@ will have a [=powerless=] hue component.
 	When changing a powerless hue component to a [=missing component=],
 	the chroma (or other measure of colorfulness, such as saturation in ''hsl''; see [=analogous components=]) is set to zero
 	to avoid amplifying floating-point noise.
-	In the case of ''hwb'' set ''b'' to ''100 - w'' or if either ''b'' or ''w'' is missing set the other component to ''100''.
+	For ''hwb'' follow these steps instead:
+		<pre>
+		1. if W + B is greater than 99.999 and W + B is less than 100
+		2. if W and B are not missing
+			2.1. set B to 100 - W
+		3. else if W is not missing
+			3.1. set W to 100
+		4. else if B is not missing
+			4.1. set B to 100
+		</pre>
 
 <h3 id=parse-color>
 Parsing a <<color>> Value</h3>

From bc100f1a1623d19054d713f5759438fcffa4d319 Mon Sep 17 00:00:00 2001
From: Romain Menke <romainmenke@gmail.com>
Date: Fri, 14 Aug 2026 09:00:05 +0200
Subject: [PATCH 4/4] clarify applicable value range

---
 css-color-4/Overview.bs | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs
index 69adb077699..7e2642c655d 100644
--- a/css-color-4/Overview.bs
+++ b/css-color-4/Overview.bs
@@ -1296,15 +1296,17 @@ will have a [=powerless=] hue component.
 	When changing a powerless hue component to a [=missing component=],
 	the chroma (or other measure of colorfulness, such as saturation in ''hsl''; see [=analogous components=]) is set to zero
 	to avoid amplifying floating-point noise.
+	Negative values are not clamped to zero,
+	this value is only set to zero when it is larger than zero but smaller or equal to ε.
 	For ''hwb'' follow these steps instead:
 		<pre>
-		1. if W + B is greater than 99.999 and W + B is less than 100
-		2. if W and B are not missing
-			2.1. set B to 100 - W
-		3. else if W is not missing
-			3.1. set W to 100
-		4. else if B is not missing
-			4.1. set B to 100
+		1. if W + B is greater than or equal to ε and W + B is less than 100
+			1.1. if W and B are not missing
+				1.1.1. set B to 100 - W
+			1.2. else if W is not missing
+				1.2.1. set W to 100
+			1.3. else if B is not missing
+				1.3.1. set B to 100
 		</pre>
 
 <h3 id=parse-color>