Tint color not working on a slab?

Hey there!

I haven't logged on here for a long time, but I got interest and started doing little projects. I want to make this kind of slab mod and all I have is a grass slab. Problem is, that when I select from the list the tint type, save it and play the game, nothing changed in the texture. I can't find anything online so could anyone help me? Thanks in advance.