[css-color-5] fix w3c#4732 with spec text and adam's example

Author: Chris Lilley

css-color-5/Overview.bs

@@ -287,6 +287,36 @@ Selecting the most contrasting color: the ''color-contrast()'' function {#colorc
 
 	</div>
 
+	The colors in the list are tested sequentially,
+	from left to right;
+	a color is the temporary winner
+	if it has  the highest contrast of all those tested so far,
+	and once the end of the list is reached, the current temporary winner is the overall winner.
+	Thus, if two colors in the list happen to have the same contrast,
+	the earlier in the list wins
+	because the later one has the same contrast, not higher.
+
+	<div class="example">
+		<pre class="lang-css">
+			foo {
+				--bg: hsl(200 50% 80%);
+				--purple-in-hsl: hsl(300 100% 25%);
+				color: color-contrast(var(--bg) hsl(200 83% 23%), purple, var(--purple-in-hsl));
+			  }
+		</pre>
+
+		The calculation is as follows:
+
+			* <span class="swatch" style="--color: hsl(200 50% 80%)"></span> --bg is rgb(179 213 230) which has relative luminance 0.628835
+			* <span class="swatch" style="--color: hsl(200 83% 23%)"></span> hsl(200 83% 23%) is rgb(10 75 107) which has relative luminance 0.061575 and contrast ratio 6.08409
+			* <span class="swatch" style="--color: purple"></span> purple is rgb(128 0 128) which has relative luminance 0.061487 and contrast ratio 6.08889
+			* <span class="swatch" style="--color: hsl(300 100% 25%)"></span> --purple-in-hsl is also rgb(128 0 128) which has relative luminance 0.061487 and contrast ratio 6.08889. This is not greater than the contrast for purple, so purple wins.
+
+		The calculated values here are shown to six significant figures, to demonstrate that early rounding to a lower precision would have given the wrong result (0.061575 is very close to 0.061487;
+		6.08409 is very close to 6.08889).
+		<!-- great example to use in WPT -->
+	</div>
+
 Modifying colors {#colormodify}
 ===============================