I personally wouldn’t go with a red velvet cake extract…I feel you could get better authenticity and additionally tweak ratios to your liking by using ingredients such as:
CAP Fudge Brownie
TFA Double Chocolate Clear
CAP Vanilla Custard
While I think there’s a little more to a “Red Velvet” profile than just red food dye in a chocolate cake, the red velvet is more of a visual effect…at the end of the day it’s just a very moist and buttery chocolate cake with cream cheese frosting.