great looking delhezi!
i agree red is the best as it brings out the best contrast, but it is somewhat unnatural. i'm guessing tan or reddish brown type color can produce similar effect as red and looks more natural, just speculation as i haven't tried it myself yet.
black and buff (kinda a sandy color i think, not sure if its same as natural) is a toss-up for me, since buff may not bring out enough contrast in some bichirs, and black can make some bichirs really ugly by darkening up the base color a little much and giving them a charcoal look. i used to think black is the next best thing after red for bichirs, not so much anymore. your del looks fine on black though