Nomad, I think the camou scheme came out good, definitely looks Wehrmacht. As suggested, just needs some areas tidied up. I'd use a no.1 size brush, and use a stipple motion to avoid paint build up and it will also help mimic a slighly feathered edge that you already have. So don't load the brush with paint, keep it light and slowly build up. You might even want to thin the paint a bit.
Bill's Marder original base colours were pretty dark too, well accept for the dark yellow. He lightened it to make the other two camou colours pop - this though is artistic license , and not something soldiers in the field were concerned with.
You can find his build log here:
http://www.bpmodels.net/Model/Album/phpBB2/viewtopic.php?t=168
Of course, if you want to do the same thing, it's still possible. Lighten up your desert colour by mixing in white, or buff, or even a very light grey. Apply it with a brush over the existing desert camou you already have. Just use the above stippling method I described above.
regards,
Jack