I am almost done my Jaster armor and after spending literally hours looking through the Open Seasons comic, I've chosen to go with a pewter rub'n'buff. The armor is the comics is darker than the Jango armor you see in the end of the comic yet has a very metallic reflective quality. The pewter is darker than than the silver rub'n'buff. I used flat black primer, wet sanded with 400 grit and then applied directly.
I'm using a red automotive paint that gives the illusion of red anodized metal for the shoulder bells.
If you really want to be accurate with this suit, be sure to use a red lens for the visor. I'm going to use a clear visor with red light gels over top to get this effect though ideally I'd like to get a red mirrored motorcyle helmet visor for this.
I tried the pewter rub'n'buff over a silver base coat and it did indeed come out way too silver. The black primer really darkens the pewter up. If it's still a little light in the end, I might dust the armor down with some powdered artist's chalk. I suppose even a boot brush with a tiny amount of black shoe polish might work. Hard to say.
The artist for the comic book is too inconsistent throughout the panels. In some it looks like a dark grey, and in a few its a dark blue. I would choose whatever color you like best. I have done the flat grey in my early Jaster versions and ended up with a dark blue metallic.