It has less code now but more versatility. This time the lookup table handles what the OpenGL/Hardware option used to and it allows you to blend the saturation styles together more freely. As this is just a trial, I've only ported DooM's palette so far. There is a primitive attempt at increasing the Colourmap's colour depth which means smoother fading of colours as distance changes. The side effect of such is that odd colour bands are softened and spread over normal colour areas. For this technique to work effectively those will have to be dealt with beforehand in the future.
Download V2.0
An almost complete rewrite with many optimizations as well as including individual Lookup Tables for six common palettes.
Troo Cullers brings the colourmap effect from DooM's early days and mixes it with GZDoom's hardware renderer. Conversely, it approximates how the High Colour mode might have looked if it were ever implemented. Plus if you ever wanted to see how your console version would have looked with a colourmap then here's your chance!
I should note that I no longer own a copy of HeXen and have never owned Heretic so they are as yet untested. Let me know how it goes

The center pane demonstrates the colourmap from the left-side 8bit image after it's applied to the right-side 24bit version.
Special thanks to Rachael and dpJudas for their guidance and also Romain Dura for the colour blending code.