rpoca

Photoshop, GIMP, CSS, etc. ara just tools. You should first get some good taste. It can be learnt. And it will pay well in the future (for example, you'll avoid hiring a bad designer).

Learn a bit of color theory, as to avoid creating horrible mashups. Don't trust just pre-baked palettes. The proportion you use of each color is even more important.

Learn some composition, read a pair of introduction books on design. The more you learn, the better.

Good design is hard to come by. In programming and in arts.