RR rarely pop out of BV, but *can* pop out of BR.
Blue Rili have been bred to reduce/eliminate the red.
BV have a mutation that causes the red to fade away- usually around juvie age. You would be surprised how many sellers don't even know that. In fact, because the final coloration looks very much the same, people often assume they are, when in fact they have different genetics.
Now, having said that, you do see the occasional BVR (Blue Velvet Red). That's usually less than 1%. The red lasts until adulthood, but even then the BV mutation can still make it fade away given time.
This is why I personally chose not to use BV in the creation of BBRR. My own theory is while the first generation would probably not have the red fade (because the mutation is now split), by the 2nd generation and beyond the possibility of the mutation showing up again would be very frustrating. Just imagine you finally have nice BBRR and your stock randomly loses the red, while some keep it. It would take years to try to breed that out, and even then you may not be successful. (?)
However I suggest that people try their own theories about what they believe is best, and let us know your trials, and results. Both good and bad. IN this way, we can continue to learn more.
Right now Rachel (MsJinkzd) has a sale on RR for $2 each. She's a member of TPT, has an excellent reputation and it's a good price.
I over sold on my mixed rilis and am now waiting for my colony to build up again. Perhaps by November.
Aquabid also has RR for sale. I personally stay away from those ads that say BR/BV as to me it is evidence that a seller doesn't know the difference...but then again, there are some that swear up and down there is no difference- so make up your own mind.