Are you looking only at what this pair will produce or are you planing to breed those babies?
Unless the female you add is a violet carrier your male will basically breed like a standard (with the chance of less quality babies) So adding a Black or Brown Velvet will just give you v/c standards or v/c velvets. The color won't change from the Violet. If you are not planning to breed the babies I wouldn't suggest it because violet just brings down the quality.
If you are trying to eventually breed those Velvet violet carriers back to Violet to get a Violet Velvet, that is a different story. I have done a lot of work with Violets and created a beautiful champion line and it was hard. I found the best way was to Always breed Violet Carrier to Violet Carrier whenever possible. (And those were show quality). Breeding the carriers gives you all of the benefits of the standard, but gives you the possible violet outcome.
Also, you do need to be careful when you put two females together, especially with a male in the cage. Females are territorial and will fight to the death. Even if you can get them together you could have problems when a girl gets hormonal from pregnancy and then again when one delivers.
