How much white white would i add to a recipe of Antonia74 Royal Icing?

Thanks

I add 5-6 drops of the brite white for every cup of powdered sugar. I've found this works pretty good for me.

I add it until it seems right, but I also use a clear all-natural vanilla extract From Spices Etc and that really helps a lot as it does not tint the RI. This way I use less whitener. Also, when I do add white, I prefer Americolor Bright White.