This banner is limited to 16 colors, sucky,
so you have to get creative with your skinning.
Actually it is possible to create banners with way more colors than 16. I succeeded in creating some tests with more than 128.

The process is to :
1) create a banner in full colors RGB mode.
2) reduce to Indexed Color
3) Modify your Color Table so #1 is main background, #128 is hover font and #142 is normal font
4) save optimized as a 8-PNG without changing depth color and you're done with a hi quality skin !
palette :

Result :
