Back in the RTB 1.x days, Bleh had a way to randomize particle colors
colors[0] = getrandom(0,1000) / 1000 SPC getrandom(0,1000) / 1000 SPC getrandom(0,1000) / 1000 @ " 0.500";
colors[1] = getrandom(0,1000) / 1000 SPC getrandom(0,1000) / 1000 SPC getrandom(0,1000) / 1000 @ " 0.0";
But the randomized colors only change every time you either re-execute the file, or restarted your server
Maybe there's a script you can do that would randomize the RGB values