Kind of a broad topic...the basic thing is that the big transition in uniforms and equipment occurred in 1910 when the Germans went over to the grey for field uniforms. Before that, uniforms were a lot more colorful. For infantry, and this is a BROAD generalization, tunics were a dark blue with matching pants (white pants were worn in the summer months). There are a number of references out there with more specifics (I'm at work so I don't have access to my library) and there are quite a few variations (it gets worse with cavalry).
If you're looking at pre-1910 uniforms, you're going to have to look at an original in order to draft the necessary patterns- there's nothing commercially available, as far as I know.
Probably one of the best original sources to go to is Moritz Ruhl- he publised a number of "aftermarket" uniform guides (I have a reprint of the one covering all the new grey uniforms so it wouldn't be much help if you're looking for earlier stuff). The one thing you'll find out about German uniforms is that the Germans were not big on putting uniforms regulations in a central place and using pictures. Lucky for us, there was a thriving private purchase market for both enlisted and officers and this helps out a bit.