Regular eggplant (
Solanum melongena) and the common red eggplant (
S. integrifolium) happen to have the same number of chromosomes (24) and will cross according to the research I've been able to find. The cross only works one direction, though I don't recall which way.
What I haven't been able to find is any photos of the F1 plant/fruit, or discussion of what happens in the F2 generation.
I have seeds for both types and hope to set up the cross next season. If I'm daring, I might setup inside lights to do grow a couple of the F1 plants over the winter so I can grow out the F2s the following growing season... time will tell.
Ah, found the link...
http://rd.springer.com/article/10.1007/BF00133296