[css-color-4] Add Lab <-> CMYK summary w3c#4647

Author: svgeesus

css-color-4/Overview.bs

@@ -2292,6 +2292,26 @@ Converting Lab colors to RGB colors</h3>
 		<li>Convert from linear-light display-p3 to display-p3 (do gamma encoding)
 	</ol>
 
+	There is sample JavaScript code for this conversion
+	for various RGB colorspaces, in [[#color-conversion-code]].
+
+<h3 id="cmyk-to-lab">
+Converting CMYK colors to Lab
+</h3>
+
+	Conversion from a calibrated CMYK colorspace to Lab
+	is typically dones by looking up the Lab values in an ICC profile.
+
+<h3 id="cmyk-to-lab">
+	Converting Lab colors to CMYK
+	</h3>
+
+	For print,
+	Lab colors will need to be converted
+	to the colorspace of the display.
+
+	This is typically dones by looking up the CMYK values in an ICC profile.
+
 <h3 id='lab-to-lch'>
 Converting Lab colors to LCH colors</h3>