Not too sure how vibrant you want the metallic look, but my daemons were quite metallic looking that I did a while back.
Those are basic daemons.
Painted them runefang steel first.
Washed with badab black / nuln oil.
Dry brush heavily with necron compound.
Then 2-3 layers of drunchii violet.
Makes them a pain in the arse to get a pic of, but makes them look like they are metallic purple quite well.
Other than that, eyes and bolter both look solid to me.
I'm always a fan of bright marine eyes that stand out.