Did you ever put clothing items away i.e., like an heirloom wedding dress or a christening outfit only to find out that the creases had turned a bit yellow? Well I have a solution for you but only if you can be real patient.
Take the item (you don't even have to wash it) and hang it real secure on a clothesline. Leave it there during rain, snow, sleet, what ever weather it encounters. I did this with a cotton wedding dress that was over 40 years old. I originally hung the dress out in October. and left it there for about 2 months. Keep checking to make sure that the clothespins that you use are nice & tight. Well "lo and behold" the yellow areas came out. This remedy was told to me by a woman that specializes in antique linens. Happy bygone days to yellow marks.