Derby apparently was camouflaged, although I couldn't tell from the one picture I have of it. Dragon would have you use od and earth brown, but most of the reference I have seen say the 2nd Armored Division used od and black. So I used the blu-tack trick I tried out on the Stug IV and Jagdpanzer to mask off the camouflage of the OD areas so I could spray the black. must confess I copied the pattern from another modeler, Jim Lewis, has a 1/35 scale buildup of Derby om his website, Guntruck. I particularly liked the camo pattern he used on his Derby build, so I copied his. I still have some touch up to do, but I'm pretty happy so far.
As for the Horch I laid down a coat of Tamiya German Grey lighted with a paler grey. I also found a great online reference Vincent Abbott's Smugmug site has a great album with 100 shots of the Horch, and will be a great resource for the second kit.