[GUI Engine] Fix the TRANSPARENT definition issue.
@@ -72,7 +72,7 @@ extern const rtgui_color_t default_background;
#ifdef TRANSPARENT
#undef TRANSPARENT
-#define TRANSPARENT 0
+#define TRANSPARENT RTGUI_ARGB(0, 0, 0, 0)
#endif
extern const rtgui_color_t red;
