[css-color-4] Add back helpful reminder about what the axises mean, in a parenthetical this time.

Author: tabatkins

css-color-4/Overview.bs

@@ -1679,11 +1679,11 @@ Specifying Lab and LCH: the lab() and lch() functional notations</h3>
 	The third argument is the hue.
 	It's interpreted identically to the <<hue>> argument of ''hsl()'',
 	but doesn't map hues to angles in the same way.
-	Instead, ''0deg'' points along the positive "a" axis,
-	''90deg'' points along the positive "b" axis,
-	''180deg'' points along the negative "a" axis,
-	and ''270deg'' points along the negative "b" axis.
-	If the provided value is is negative,
+	Instead, ''0deg'' points along the positive "a" axis (toward red),
+	''90deg'' points along the positive "b" axis (toward yellow),
+	''180deg'' points along the negative "a" axis (toward green),
+	and ''270deg'' points along the negative "b" axis (toward blue).
+	If the provided value is negative,
 	or is greater than or equal to ''360deg'',
 	it is set to the value modulo 360.