Did you use the p-aminophenol base or the hydrochloride? I never had it turn brown unless perhaps the p-aminophenol was partly oxidized to begin with. When you add the powder to a hot solution, the powder may be heated enough as it enters the solution to be oxidized by the time it is immersed. If there is some water in the glycol, the hot air above its surface will be humid, increasing the possibility of oxidation.
You were measuring Fahrenheit weren't you?
Be sure you use the base when you are dissolving in glycol or TEA.
I don't remember ever trying to see how much I could dissolve because, other than for Rodinal, which I always make in water, I don't need high concentrarions of p-aminophenol in glycol or TEA.
I make a slurry at room temperature when I am mixing in glycol, whatever I'm mixing. The main purpose of the heating is to reduce viscosity and thereby speed up the dissolving. When I'm using TEA, I warm it enough so I can stir it, stir in the powder, and then raise the temperature.
P-aminophenol generates intense colors on oxidation. A small amount of oxidized p-aminophenol can color a much larger volume of solution, yet not cause a perceptible change in the activity of the solution. Rodinal is a witness to that fact.
5 g of ascorbic acid would have been a better bet than the metabisulfite IMHO.