in wxFormbuilder 3.3.3-beta:
Not all wxWidgets controls correctly use their parent window' background color, but hard-code a different value. E.g. wxHyperlinkCtrl, as can be seen in wxGTK on Ubuntu.
Now to solve these issues and others, I need to set background color of various controls to "Window" in "Object Properties" on the right. Unfortunately wxFormbuilder makes no visual distinction between "no value" and "Window". Effectively I first have to change background color "window" (which is in reality "no value there") to some arbitray other value, then change it back to "window" (now it's really "window", as can be seen in the .fbp file).
This is the same problem like in another tickets related to font: Background color needs a "default" value in Object Properties. Currently it is not possible for the user to see if there is no background color set or if it is set to "window".
Note that the difference between background color "window" and a control's default color is generally not visible on Windows, but becomes a GUI bug on other platforms using GTK. Therefore the "Object properties" dialog is the only place to actually see what color has been set during design time.
The same problem naturally applies to the foreground color as well.