Just got new bead blaster at workhinkingThanx
Mot
edit: I would like to find a way to mask off lettering too.

Bad idea, unless you are planning to have it re-anodized.

The color of the upper/lower is the anodizing which has been dyed. It is not a paint, or something that was applied and can be easily removed. If you remove the color, you have removed the anodizing, you have taken away the protective shell and exposed the softer, raw aluminum. Once the raw aluminum is exposed, it is subject to corrosion and is more susceptible to damage from chemicals.

You also have to be very careful that you don't remove the anodizing and allow the blaster to start damaging the raw aluminum by expanding/egging the hole.

If your upper/lower is in rough shape, you still have a couple of (better, IMO) choices. Spray them with Duracoat/Norrell's or one of the other available gun finishes. These apply well over the existing anodized finish. Or, have it  done professionally, by having it chemically stripping, re-anodizing and re-dyed.