Someone (user Pr0eliator from cdprojektred forum) suggested to change the texture color of the drowners.
So I tried and did some recoloring of all the textures and changed drowners, drowned_dead (high level drowners), mucknixers (skellige's drowners) and underwater drowners.
But while testing I saw that dismembering a drowner would make it use the common drowner texture for the severed limb, creating an ugly effect if the colors of the 2 textures were too different.

Vanilla pic of the problem: http://imgur.com/ltUmrU0

So this is what we finally agreed on.

Drowners: gave them a more greeny-grey feeling rather than vanilla blue.

Drowned_dead: made them similar in color to normal drowners, with some red to reflect their high level.

Mucknixer: Gave it a more reddish look.

Underwater drowners: changed their almost teal color to a more grey-blue neutral one.

Modded pic of the dismembering: http://imgur.com/1VjW9Be

The difference in color is still present while dismembering but if you didn't notice it until now, you probably won't care about it. :)