You should't flush it, tryptamines can turn brown pretty quickly, but only lose a bit of potency and still be good. I have had brown 4-AcO-DMT that still worked and produced a good trip. I have some brown AMT that is just fine. I would treat it like it's fine, and it may be you need a slightly higher dose, but don't throw it away.
But yes, an amber vial in the freezer will prevent or drastically slow further degradation. You should store all tryptamines that way. When you remove them from storage, make sure you let the vial warm to room temperature before opening it, as failing to do so will moisturize it.