[Lazarus] Forms Color on Linux

[Luiz Americo Pereira Camara]

Michael Van Canneyt wrote:
> In view of all the double buffering, I'm not surprised that the GTK2 version 
> works slow. Double buffering is evil (tm) unless you do moving graphics.

FYI double buffer is disabled for all controls in LCL-Gtk2. This is one 
of the reasons of the difference between pure gtk2 apps

Luiz