[css-color-4] Reword color interpolation to stress conversion to a common space first.

Author: svgeesus

css-color-4/Overview.bs

@@ -4765,9 +4765,13 @@ Interpolation</h2>
 	animations, and
 	color mixing and color modification functions.
 
-	In general, interpolation between <<color>> values
-	occurs by linearly interpolating each component of the computed value of the color
-	separately, in a given color space which will be referred to as the 'interpolation space' below.
+	Interpolation between <<color>> values
+	occurs by first
+	converting them to a given color space
+	which will be referred to as the 'interpolation space' below,
+	and then
+	linearly interpolating each component of the computed value of the color
+	separately.
 
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