I am doing the typical and well-known trick with a "darkness" layer set to Subtract and illuminating the scene with circular light gradients, and that's cool and all but it only allows white lights.

Is it possible to somehow add coloured lights using this technique? I tried adding some coloured lights (like a blue glow or maybe slightly red-yellowish for burning torches) but it just ends up looking weird.

(It's the lighting technique similar to http://www.sketchy.co.nf/downloads/Lights.mfa )

EDIT: I figured out how to make coloured light blobs that don't mess up when overlapping each other:

Make a coloured gradient that goes from whatever colour to black (so a circular gradient that goes from blue -> black for example), then use that same graphic as the alpha map by grayscaling it first and then pasting it into the alpha channel of the object.

Finally, give this object the Subtract effect. Be sure this object is placed in the same layer as the darkness layer!

Seems to work and they all overlap each other fine without messing up the lighting.