http://necros.slipgateconstruct.com/downloads/ne_ag_LightMHColourR2.zip
This is based off of mh's coloured light/multicore tweak of aguirre's light utility, so it has all the good stuff.
Two new command switches are added:
-fakeGISun2
Makes sunlight2 cast additive light in a full sphere (as opposed to a dome).
-fakeGIMode
Makes sunlight2 not require skybrushes (ie: the light comes from the void)
NOTE: REQUIRES -fakeGISun2
Also note you need to set the worldspawn keys 'sunlight' to '1' otherwise it's not activated at all and the 'sunlight2' settings should be low, 2 or 3. 4 is pretty bright.
I basically just turn off the check that requires sunlight to pass through a skybrush first, so with -fakeGIMode, the sunlight comes from the void.
Source included. Some small changes to LoadEntities() and TestSky() and maybe one or two other tiny things I've forgotten.