Well after almost 3 hours of attempt, this is really no way that ButtonBar works.
To be sur of the change i made it red and the only place where it shows then is on the Wardrobe.
It seems that the Blue bar i am looking for is also used in the active skill tab for the search button.
And for the RAid windows, it seems that it does not support to be transparent. I made about 50 different test with different colours, so the panel you told me is the good one but for a reason i dont understand, the transparency apply correctly to the Friends, Kinship, Lock raid window, and fellowship window but not the raid group one.
Thank you anyway for your help, i guess i am blocked there at least for now
