Welcome to the Official BlackBerry Support Community Forums. This is your resource to discuss support topics with your peers, and learn from each other. New to the forum? Please visit the ‘Getting Started’ link below.
I believe it's not currently possible, but note that they are considering ways to "theme" Cascades. The initial approach may be little more than some color customization, but I would sort of expect that once they have even that in place it will be possible to adjust it programmatically.