blue velvet is a mutation that fades the red from a rili by the time they hit juvi, while blue rili is selectively bred to reduce and eliminate the red.
Personally I wouldn't mix either one if you want a strong specific coloration and pattern. I'd just cull.
BUT If you just want to have fun and have a tank of assorted colors and patterns, including cherries and wilds, you can keep any colors you want in there.
