I like them alot!
For the bases light brown tufts sound great, but i wouldnt change the rim colour,
black looks good and i feel like if you do them brown it would just be brown in brown.
To make the models pop more i would either go a bit lighter on the eyes or the drug tubes (if they are drug tubes for you).
Maybe if you are into it you could paint the tube thingy in the rifles in a brighter colour but honestly i dont think its missing much, the light blue goes really well with the purple armor^^