We are running a project in Zytel GF33%/ST nylon blend and the parts require a 100% dull finish. Has anyone used dulling agents or colors ( concertrate or liquid) to obtain a dull finish on GF Nylons

Kelly,
I personally have not used any agents or colors to dull down GF Nylon's. However, I have dulled GF Nylon's through running a cold mold versus a warm or hot mold. When I say cold, I mean 55 degrees F. This provided me with a dull yet clean finish.
Naturally, this may cause issues if you do not perform a solid process study first. As your technicians may have other issues during startups.

The cold mold like Jerome mentions will bring more glass to the surface as apposed to a hot mold and resin ritch surface. Is there too much gloss if a stipple or mat finish is added to the cavity and core?

I feel that a cooler mold, not down to 55°F since your running a milspec part out of ST nylon, as well as a grain change to the mold will be the long term solution. With that much filler I would suspect that the part would appear more silver if the steel temp drops too much. Plus you will lose impact and so on.
Rick.

Rick, that is how we normaly would expect a GF nylon to react, however, I have found that at 55°F the finish on the part (no grain) is a uniform dull black (no "silver" or glass look at all). The impact was not affected either, as our destructive testing resulted in a mean average of the same as running the tool at 100°F. This is just what we found with our process and tooling set-up. I am certain this would not be the same on a global scale, however, I would highly suggest giving it a try as the "cost" is only time.

Does the tool has texturing on the moulded/required surfaces?, If not consider it with dull/dry/matt finishes on the tool. it could be done on the existing texture finish also.
Should consult your local texturing company, It is not too difficult to acheive it.

With texture will make it dull, but still need low mould temperature, and this need try, different mould will have different result. And I just suggest you put the injection gate a little bit bigger than other materials. If this mould was sub gate you can put the gate diameter from 1.5 to 1.8mm, this will help the fillings, especially for Nylon.

I personally don't like the cold mold option, as a cold mold will introduce more molded in stress. Also, the dulling agent idea is probably not acceptable without government approval, as they tie you down to physical properties, which could be influenced by adding any additive. The texturing of the mold is the best option of the ones mentioned, but could present problems at ejection if the texture causes a undercut situation in areas of the mold at eject.
We have used a subsequent sandblast operation for this purpose, it will also be beneficial as a stress relief to the part. I know, most are hesitant to add another operation, but sometimes your hands are tied.