If you read the explanation here : Custom colouring for Themers, as linked to in this sticky ...you'll likely come come to the conclusion that you don't actually want to re-enable the old legacy colouring, but by all means try it if you're curious.
In modern themes the tint depth and location is set by the transparency depth and location within a few images; either do some image editing or ask the theme maker for alternate image files.
How to change color tint on themes where the option is greyed out?
Linear Mode
