Are you painting just one miniature or a whole regiment? Also, it probably would be best for you to post a picture so that people can see what you have done wrong and remedy the problem.
A good quick and easy way the paint orc cloth I have found is to start with scorched brown, drybrush dark flesh, wash with a dilute brown ink all over, and add highlights to the creases with dark flesh. This will give a fairly dingy brown but without being uninteresting.
Anyway, hope that helps, and good luck with your orc/s
Cheers,
Tom