Subject: Why do multiple mutational fruit flies appear to have darkened wings?

hi 
this is a question from my lab session for a general biology module. 
Of the many mutations we observed in fruit flies, one was a multiple mutant 
with white eyes, miniature wings and forked bristles. Apparently one of the 
characteristics of the multiple mutant is that the surfaces of the wings 
appear to be darker than those of the wild type. So, what is the reason for 
the darkened appearance of the wings?
Thanx! 

Re: Why do multiple mutational fruit flies appear to have darkened wings?