I've never seen solid black guppies before. I think it would be really cool if you found some in turquoise blue to put in with them for a nice contrast in your display. Unless you're trying to breed this strain, of course.
Guppies are so beautiful, but for some reason I have never been able to keep any fancy ones alive. Endlers will breed for me to the point that I don't even want to keep them anymore, but fancy guppies die within days of bringing them home. =(