Added paragraph explaining the use of hex values

HTTP-request-API.md

@@ -47,7 +47,9 @@ Parameter | Value Range | Description | Since Version
 &SR= | 0 or 1 | Set Primary/Secondary color to random hue | 0.4
 &SC | none | Swap primary and secondary color | 0.4
 
-Note hex values need to be prefaced with #, h, or H.
+### Use of hex values
+
+Hex values need to be prefaced with #, h, or H. The normal format is `RRGGBB`. If the led strip is RGBW, the hex format is `WWRRGGBB`. Note: In the UI the format is `RRGGBBWW`, so the values cannot be copied without a transformation.
 
 ## Notifications