Yeah, I usually see it for seconds a year. If I saw it often enough to worry about theming it, I'd rather spend my time on fixing whatever caused me to have to see it so ofen.
Look at the screenshots. They are all about booting multiple OSes or distros, and should make sense for those who switch between them often. ("Why" is another question.)
I think this is the kind of thing I would do If I had to choose between OSs with frequency, either home lab/experimentation or linux for stuffs and windows for games kind of scenario.
So there is nothing to fix, the nice choice screen is a feature.
You'd spend more quality time with it if it looked beautiful. Think about it going up and down those menus for hours on end. Quality grub.