scrollbar and gnome3

[Marc Blanc]

Hello,

i am usually using WindowMaker but gnome is installed because Gthumb
and other soft which need gnome. After upgrade f14 --> f15 the scrollbars
in WindowMaker are blue like this picture :
http://www.flickr.com/photos/flore-alpine/5781657799/
is it possible to change this color and how ? I have changed the themes but
it's operating only in the gnome interface no in WMaker.
Thank you.

-- 
M.B