[css-images-4] Add example of missing hues when interpolating with neutrals, w3c#4928

Author: svgeesus

css-images-4/Overview.bs

@@ -1764,6 +1764,25 @@ Coloring the Gradient Line</h4>
 	the color space used for gradient interpolation
 	is the default interpolation color space, Oklab, as defined in [[css-color-4]].
 
+	<div class="example">
+		For example, given the following gradient definition:
+
+		<pre class="lang-css">
+			linear-gradient(in oklch, red, #888, green)
+		</pre>
+
+		the conversion of the neutral #888 to oklch
+		gives a missing hue component:
+		<span class="lang-css">oklch(0.6268 0 none)</span>
+
+		and thus, in the first gradient segment, 
+		the hue is taken from red, 
+		which is <span class="lang-css">oklch(0.628 0.2577 29.234)</span>;
+		while in the second segment 
+		it is taken from green,
+		which is <span class="lang-css">oklch(0.5198 0.1769 142.5)</span>
+	</div>
+
 	By default,
 	this interpolation is linear--
 	at 25%, 50%, or 75% of the distance between two <a>color stops</a>,