Comment 75 for bug 491521

Andrea, you need to actually look at GdkColormap or the GdkVisual directly and determine if it's an RGBA colormap. You can't compare the return value of gdk_screen_get_default_colormap() and gdk_screen_get_rgba_colormap(), because they'll be different values even though they're both RGBA colormaps.

The reason for this is because we're planning to do a further optimization once we get a new EWMH hint spec made official. But basically we want to be able to differentiate between widgets that are set to RGBA by either gtk_widget_set_colormap() or which are told through the theme that they're RGBA as opposed to widgets that are only RGBA because it's they inherited the default and don't actually draw any RGBA.