It seems to happen as a result of diet, I think. Diet seems to effect some roaches lightness or darkness and not other species. Olivia (aka BugChick) posted a good example of some Harlequin roaches that had the reverse problem. Dont have the link handy but you could find it here on AB.
Matt K, that's not a result of diet it's just natural variation.
Herp1- You'll probably start getting more of them appearing in your colony.
My original dubias were pretty consistently patterned. A couple of generations down the line and I've got a wide variety in the same tub. They range from almost solid black with very little pattern to being heavily patterned like the one above with yellowish or dark reddish colors. Some of the nymphs I'm raising now are looking different than any I've raised before so my next generation could produce some very funky looking bugs. I've heard others are starting to see the same thing.
Once you have about 10,000 plus you will see many variations. I've even seen strains that are much smaller in size to very dark to very orange. I guess since this has just been a main stay feeder species I've never really tried to selectivly breed them. But then again many species so variations from colony to colony so who really knows why.
i have about 55 adult females and only four males. i did a little over feeding oops... but any way some of my females are black with orange is that anything special? i'll try to post a pic tomorrow with one normal and one black side by side.
That should be interesting! Did any of the females mate with the males? That could be why. But then again this is just a theory since I've never kept them and my mom will make sure that that will be the last thing I do.
She can't stand the German Cockroaches in our house when we have them so what's going to make her like these? Plus they're much bigger then the German cockroach so she's likely to hate them even more. ;P