[css-color-hdr] Added section on interpolating colors parameterized by headroom w3c#11616

Author: svgeesus

css-color-hdr-1/Overview.bs

@@ -507,6 +507,15 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 
 	</div>
 
+<h3 id="#headroom-interpolation">
+	Interpolating colors based on headroom
+</h3>
+
+	To interpolate between a color <var>c1</var> at headroom <var>H1</var> 
+	and a color <var>c2</var> at headroom <var>H2</var> 
+	when the target headroom is <var>H</var>:
+	
+
 <h2 id="color-function">
 	Specifying Predefined and Custom Color Spaces: the ''color()'' Function
 </h2>