Thank you, it totally worked.
As you may already guessed, with buffer_fade disabled the picture doesn't look so real after some time (those dark violet stains, oh my).

Well surely this is just the thing you get when trying to override safe limits added by developers.
But if you don't mind, I'd like to dig a bit deeper:
- is there any way to slow down fading of those marks without disableing it at all?
- if not, is there any way to limit possible "thickness" of the marks so that they wouldn't become crazy violet smudges? (Maybe some another hidden variable that limits possible mark saturation from 0.00 to 1.00?)
But still thanks a lot for your efforts, guys.