Fix colour not being sent properly by backend (#81)

Reviewed-on: #81

backend/colour.go

@@ -28,3 +28,7 @@ func ConvertStringToColour(colourStr string) (int, error) {
 	}
 	return colour, nil
 }
+
+func ConvertColourToString(colour int) string {
+	return fmt.Sprintf("#%06X", colour)
+}