[css-color-4] Fix note about double positions making a stripe. Add note about color before/after the stop lists. #11381

Author: tabatkins

css-images-4/Overview.bs

@@ -1878,8 +1878,11 @@ Color Stop Lists</h4>
 	A <a>color stop</a> with two positions is equivalent
 	to specifying two <a>color stops</a> with the same color,
 	one for each position.
-	<span class='note'>Specifying two locations makes it easier to create solid-color "stripes" in a gradient,
-		without having to repeat the color twice.</span>
+
+	Note: Usually, this results in a solid-color "stripe"
+	between the two positions,
+	but using a ''longer'' <<color-interpolation-method>>
+	will instead create a "rainbow" between the two positions.
 
 	Percentages are resolved against the length of the <a>gradient line</a>
 	between the <a>starting point</a> and <a>ending point</a>,
@@ -1930,6 +1933,12 @@ 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]].
 
+	Note: The <<color-interpolation-method>>
+	only affects the colors <em>between</em> stops.
+	The color before the first and after the last stop
+	is equal to the first/last stop,
+	<em>regardless</em> of the interpolation method.
+
 	<wpt>
 		gradients-with-transparent.html
 		gradient/css-color-4-colors-default-to-oklab-gradient.html