I'm not certain where in the world you're located, but feathers react to sunlight by fading. Black birds will turn brown, white birds will turn yellow, blue birds will turn light gray.
It could also be that she is preparing for her molt. Once the feathers become too damaged, they are no longer protective and she will molt them. Are her wattles shrunken? Is her comb a bit lighter red than normal?
Is she eating, drinking, laying? If she is, I wouldn't worry too much. However, it COULD be heat stress. If you're worried about this, dip her in nice cold water being sure to get underneath the feathers. Then, place her back in her pen and she will air dry. Since birds cannot sweat, this method allows them to use evaporative cooling in high temperatures.
It could also be, if her face, comb and wattles are light in color, that she has a mite problem. Flip her over and examine her vent. If you notice tiny brown bugs (the size of a pinhead) try dusting her with 5% Sevin Dust available at Wal-Mart.
Good luck! Email me if none of these answers your question!
