Put the "plasmacell_g.dds" and "plasmareceiver_g.dds" from the "glow" folder into
Data/textures/weapons/plasma

Choose one color you want and put "plasmacell.bgsm" and "plasmacell.bgsm" from the "blue", "green", "red" or "rainbow folder into
Data/materials/weapons/plasma

For the rainbow color it's a little special as it have it's own glow maps.
You need the "plasmacell_g.dds" and "plasmareceiver_g.dds" from the rainbow folder instead of "glow" folder.