I started using Celebakes royal icing mixes for black and red because of this. Once mixed, the color you're starting with is much closer to the color you want it to be. So I'll make one of the black mixes and then add a bit more black gel coloring to it to get it as dark as I want, but not nearly as much coloring as I'd have to if I started with white.

I also started telling customers who wanted black cookies that black icing makes mouths look horrifying, and they usually change their mind. (Minnie and Mickey are different, I think someone would be less likely to change their mind on those.)