Bob,
I doubt if it's a thing of secrets. Mike would probably tell ya he does it like Ed Scott does. Felt tips, paint pencils, model paints, etc. then goes over it with a clear coat after they dry.
Mikes and Ed's bows are sure nice and also it is the artistic ability to do the artistry on their bows. Yours will likely look good too, just in your own imaginative way. Some of the works are recreated from historically decorated Native Indian bows. Look them up in books and use whatever colors strike your fancy.
Rick