Neither of the posters that say they have oxidized beer note any off flavor, specifically those cardboard-y flavors that are typical of oxidation. I agree with those that think that the color change is far more likely to be a result of more stuff dropping out of suspension over time.
I think everyone's assuming that those grains are not yet milled. Is that correct? If they are already crushed, I wouldn't use them, foodsaver notwithstanding.