I use button object as checkbox and radio button in my level editor...
The level editor use HWA and I notice that "Transparent" option no longer work in this mode
The system color option give me a white background...
And if I use "custom color" the background color may vary depending of the windows theme and windows version... I want to use OS "3D Aspect button" color as background...

The quicker solution is to add the missing option to set background color of the object in the event editor. (with this, I will have possibility to pick the wanter color using the expression of active system box)