You shouldnt one minus the white one, which should work.
you could always try to multiply the white one with itself.
just fiddle around a bit untill you get something you like.
The whiter the roughness, the less reflective itll be 
You shouldnt one minus the white one, which should work.
you could always try to multiply the white one with itself.
just fiddle around a bit untill you get something you like.
The whiter the roughness, the less reflective itll be