when using opengl you can clearly see that the display depth is 16bit. if you display a number of 32bit textures with an alpha channel there is a lot van color banding.

i would love to know how to set the bitdepth to 32bit when using an QGLwidget. But i think you would loose the ability to view a thumbnail of your application when multitasking and the ability to see the alerts (like the yellowbar for the volume), since these are composited in 16bit and i don't think you can mix those.