2-3 drops of black in 8oz and then add your flake to taste. I like to use a little large and small flake and back off on the medium a bit.
You are dead on for the hi-lite though. A smidge (or less) in 8oz is killer good to me. Blue, violet, gold, orange, green, red... They all rock!
Smallies and spots seem to really kill these colors.....
Jim