About TButtonPanel:
I changed the default configuration of my Xfce desktop and I've find that background of TButtonPanel didn't match with other components nicely. So I go to the Object inspector and... There's no Color property!
So I had to change the panel colour by code at the form's onCreate event.
Why isn't TButtonPanel.Color published? I think it should be.
Also I've realised that TCustomPanel, TCustomButtonPanel and TCustomGroupBox default background colour isn't clForm. This is quite annoying in some colour schemas in Linux. I had to change all them manually to clForm.