Yep. Or you can cover it in the blue and wrap a strip of white on the bottom. But it would probably be easier to cover in white and just cut out a large circle of blue and place it offset on the top.
I haven't done this before but what I would do is put the 2 colors I want together on a piece of vinyl or mat and roll on it to join then roll it on my roller and lower it over my cake in the position I want it then smooth on cake and cut off the excess, not sure if this is the way to do it. Maybe someone who has already done it can give you more information.
thanks heaps, will see how i go