you can use every channel of colored texture as light function of the same light color.
So create 3 light sources - red, green, and blue, and use 3 material instances with masked r/g/b texture channels, as their light functions. as result - you will get colored light function.
I would like to use a light to project a coloured pattern onto a wall. Is it possible to use a texture or material instead of a block colour for UE4 lights like you can in vray?
Any image have 3 channels - red, green and blue. You need to import that image into unreal, and in light material get only specific channel.for every instance.