The color pigments are caused by the oxidation of the carcinogenic chemical compounds found within the cigar, ranging from it's growth in the soil's mineral content, to whatever pesticides are used to keep the locusts away to whatever was applied during the production processes to make the cigar what it is today.
The more important factors are:
1) Was the cigar good?
If yes then a) Does it really matter what color the ash is if you're going to smoke some more of them?
If no, then b)Does it really matter what color the ash is if you're not going to smoke any more of them?