[css-color-4][editorial] Add Oklab a,b plane diagrams for predefined RGB color spaces

Replace the CIE Lab primaries/secondaries diagrams with new ones plotted
on the Oklab a,b plane (computed via colorjs.io), for sRGB, display-p3,
a98-rgb, prophoto-rgb, and rec2020. Each diagram keeps the sRGB gamut as
a dashed comparison overlay (except the sRGB diagram itself) and adds an
8-column L/C/H legend table below the plot. The old CIE Lab figures are
left in place as HTML comments for reference.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: svgeesus

css-color-4/Overview.bs

@@ -4037,11 +4037,19 @@ The Predefined sRGB Color Space: the ''sRGB'' keyword</h3>
 			c is the gamma-encoded red, green or blue component.
 			cl is the corresponding linear-light component.
 
+			<!--
 			<figure id="fig-srgb-lch">
 				<img src="images/sRGB-prim-sec.svg" width=540 height=520
 				alt="diagram of sRGB primaries and secondaries in LCH">
 				<figcaption>Visualization of the sRGB color space in LCH. The primaries and secondaries are shown.</figcaption>
 			</figure>
+			-->
+
+			<figure id="fig-srgb-oklch">
+				<img src="images/sRGB-prim-sec-oklch.svg" width=700 height=567
+				alt="diagram of sRGB primaries and secondaries in Oklch">
+				<figcaption>Visualization of the sRGB color space in Oklch. The primaries and secondaries are shown.</figcaption>
+			</figure>
 
 		</dl>
 
@@ -4169,6 +4177,7 @@ The Predefined Display P3 Color Space: the ''display-p3'' keyword</h3>
 				</tr>
 			</table>
 
+			<!--
 			<figure id="fig-displayp3-lch">
 				<img src="images/P3-prim-sec.svg" width=580 height=560
 				alt="diagram of P3 primaries and secondaries in LCH">
@@ -4180,6 +4189,19 @@ The Predefined Display P3 Color Space: the ''display-p3'' keyword</h3>
 					P3 primaries have higher Chroma.
 				</figcaption>
 			</figure>
+			-->
+
+			<figure id="fig-displayp3-oklch">
+				<img src="images/P3-prim-sec-oklch.svg" width=700 height=557
+				alt="diagram of P3 primaries and secondaries in Oklch">
+				<figcaption>Visualization of the P3 color space in Oklch.
+					The primaries and secondaries are shown
+					(but in sRGB, not in the correct colors).
+					For comparison, the sRGB primaries and secondaries
+					are also shown, as dashed circles.
+					P3 primaries have higher Chroma.
+				</figcaption>
+			</figure>
 
 		</dl>
 
@@ -4314,6 +4336,7 @@ The Predefined A98 RGB Color Space: the ''a98-rgb'' keyword</h3>
 				</tr>
 			</table>
 
+			<!--
 			<figure id="fig-a89-lch">
 				<img src="images/a98-prim-sec.svg" width=640 height=560
 				alt="diagram of a98 primaries and secondaries in LCH">
@@ -4326,6 +4349,20 @@ The Predefined A98 RGB Color Space: the ''a98-rgb'' keyword</h3>
 					especially the yellow, green and cyan.
 				</figcaption>
 			</figure>
+			-->
+
+			<figure id="fig-a89-oklch">
+				<img src="images/a98-prim-sec-oklch.svg" width=700 height=563
+				alt="diagram of a98 primaries and secondaries in Oklch">
+				<figcaption>Visualization of the A98 color space in Oklch.
+					The primaries and secondaries are shown
+					(but in sRGB, not in the correct colors).
+					For comparison, the sRGB primaries and secondaries
+					are also shown, as dashed circles.
+					a98 primaries have higher Chroma,
+					especially the yellow, green and cyan.
+				</figcaption>
+			</figure>
 
 		</dl>
 		<wpt>
@@ -4415,6 +4452,7 @@ The Predefined ProPhoto RGB Color Space: the ''prophoto-rgb'' keyword</h3>
 				c is the gamma-encoded red, green or blue component.
 				cl is the corresponding linear-light component.
 
+				<!--
 				<figure id="fig-prophoto-lch">
 					<img src="images/prophoto-prim-sec.svg" width=780 height=760
 					alt="diagram of prophoto primaries and secondaries in LCH">
@@ -4427,6 +4465,20 @@ The Predefined ProPhoto RGB Color Space: the ''prophoto-rgb'' keyword</h3>
 					does not correspond to physically realizable colors.
 					</figcaption>
 				</figure>
+				-->
+
+				<figure id="fig-prophoto-oklch">
+					<img src="images/prophoto-prim-sec-oklch.svg" width=700 height=382
+					alt="diagram of prophoto primaries and secondaries in Oklch">
+					<figcaption>Visualization of the prophoto-rgb color space in Oklch. The primaries and secondaries are shown
+					(but in sRGB, not in the correct colors).
+					For comparison, the sRGB primaries and secondaries
+					are also shown, as dashed circles.
+					prophoto-rgb primaries and secondaries have much higher Chroma,
+					but much of this ultrawide gamut
+					does not correspond to physically realizable colors.
+					</figcaption>
+				</figure>
 
 
 		</dl>
@@ -4488,6 +4540,7 @@ The Predefined ITU-R BT.2020-2 Color Space: the ''rec2020'' keyword</h3>
 				</tr>
 			</table>
 
+			<!--
 			<figure id="fig-rec2020-lch">
 				<img src="images/2020-prim-sec.svg" width=670 height=580
 				alt="diagram of rec2020 primaries and secondaries in LCH">
@@ -4498,6 +4551,18 @@ The Predefined ITU-R BT.2020-2 Color Space: the ''rec2020'' keyword</h3>
 				rec2020 primaries have much higher Chroma.
 				</figcaption>
 			</figure>
+			-->
+
+			<figure id="fig-rec2020-oklch">
+				<img src="images/2020-prim-sec-oklch.svg" width=700 height=594
+				alt="diagram of rec2020 primaries and secondaries in Oklch">
+				<figcaption>Visualization of the rec2020 color space in Oklch. The primaries and secondaries are shown
+				(but in sRGB, not in the correct colors).
+				For comparison, the sRGB primaries and secondaries
+				are also shown, as dashed circles.
+				rec2020 primaries have much higher Chroma.
+				</figcaption>
+			</figure>
 
 		</dl>
 		<wpt>
@@ -8283,7 +8348,10 @@ Changes</h2>
 	<a href="https://www.w3.org/TR/2025/CRD-css-color-4-20250424/">Candidate Recommendation Draft of 24 April 2025</a></h3>
 
 <ul>
-	<li>Avoid referencing "prepare for conversion", just state directly 
+	<li>Added Oklab a,b plane diagrams for the sRGB, display-p3, a98-rgb, prophoto-rgb,
+		and rec2020 predefined color spaces, alongside the existing CIE Lab diagrams
+	</li>
+	<li>Avoid referencing "prepare for conversion", just state directly
 		(<a href="https://github.com/w3c/csswg-drafts/issues/14049">Issue 14049</a>)
 	</li>
 	<li>Clarified that the computed value of a deprecated system color