it actually is no different, except i make the brush more translucent and apply it many more times. its still just oldcolour*(1.0f-opacity)+brushcolour*opacity. just opacity is much smaller and done many times.
it has a bitcrushing effect on the colours, its really nice. Ill have a decent picture to show tomorrow, hopefully - at the moment the pictures here are pretty crap, ill use it decently tomorrow.
note you can get the same effect in say gimp, (just put opacity to 0.5%, thats how i first worked this out!) it just takes ages to get anywhere, this program helps speed up the process and importantly lets you work backwards and forwards with the effect.