Thanks for the credit. I made my control "themed" on purpose, not because it had to be that way (as you've demonstrated), but if people want to be able to specify their own colors etc, I'll certainly add that ability into my GroupLayout control.
I still think it's a bad idea though, because when people change themes, their chosen colors will probably need to be changed manually (not such a problem if you have one or two, but can you imagine the effort required if you have 100's of them in multiple screens throughout the application), whereas when a control is themed it changes automatically. That's why the built-in controls are all themed.
Thanks Yann. When I started to work on it, I too understand the reason why you chose to theme the control. But the theme I'm using (Infragistics) is totally washed up and your control looking 'pale' on it. That was one of the reason I started to look into this. I also started to work on the third control where I can pass the theme name, same like Xaml. Got frustrated with Multiline/Color editor part and forgot that one.