[css-color-4] more exposition

Author: svgeesus

css-color-4/Overview.bs

@@ -2438,7 +2438,8 @@ Profiled, Device-dependent Colors</h2>
 		An intense green is provided in prophoto-rgb space.
 		It has a first fallback, which is the same color in display-p3
 		in case prophoto is unsupported. The color is in gamut of display-p3.
-		Lastly, a desaturated sRGB fallback is provided.
+		Lastly, a desaturated sRGB fallback is provided
+		(desaturated, as the original color is outside the sRGB gamut).
 		<pre class="lang-css">color(prophoto-rgb 0.4835 0.9167 0.2188, display-p3 0.3499 0.9800 0.1399, rgb(33.44% 96.68% 21.07%))/pre>
 	</div>