Ok, so...
ink0 is used to get a mask for the sprites, and is also the raster colour.
ink1 is pink (used for skin and because it's girly.
ink2 is white, because spanish have a fetish for houses painted in white.
ink3 is grey, which is bad and should have been black instead.
the "HUD" (score zone) seems to have a completely different set of inks, with pastel magenta, yellow, black and grey, while the 3 "game window" raster zones seems to only change one ink (ink0) at a time.
durng the menu (out of game) inks are different too.
there is a light green or a dark red used, but it doesn't change a lot of things (because it is not in game)..
the 3 raster zones are from up to down : pastel blue, medium blue, dark blue... which is quite usable actually.
As I told, the tileset (backgrounds) would need to be inverted again... but those tiles come in many different sizes so a proper complete sheet would be great.
@syx : oops sorry, good old hacking and Graphics mockups reflexes...