:I wouldn't say that! Lots more black milks are produced than indigos...they are just pretty popular right now and sell pretty quick.
I have not kept them but they are nice snakes that thrive at cool temps.
I think the major differences you are going to see as a keeper are:
1- indigos are MUCH larger on average 2- black milks are going to act like, well, a milk snake...secretive , shy, etc. Indigos are a lot more active, alert and have more "personality" If you have smaller caging to work with...then he mliks are a better bet. Indigos need space.