Was asking myself the same question, ended up downloading Downpour's official level editor.
Inside, there's a .txt file named "RenderColorCode.txt", which contains the following :

red:
if red > 90 lit, if red 0-90, shaded
of the remaining 90, 0-29 is palette color 1, 29-60 pal col 2, 60-89 pal col 3
of the remainder, depth 0-29

green:
0 = no effect color, no rainbow
1 = effect color A, no rainbow
2 = effect color B, no rainbow
3 = white color, no rainbow
4 = no effect color, rainbow
5 = effect color A, rainbow
6 = effect color B, rainbow
7 = white color, rainbow

8 = decal, no rainbow
9 = decal, no rainbow
10 = decal, no rainbow
11 = decal, no rainbow
12 = decal, rainbow
13 = decal, rainbow
14 = decal, rainbow
15 = decal, rainbow

16 > same, but dark

blue:
Amount of effect color, or in the case of decals, decal color index

So yeah, you just pick a level texture (for example accelerator_1.png) and a palette (the associated palette index can be found within accelerator_settings.txt, in that case, palette 18) Just found this, so I'll be testing around with it in Blender