Hi Nomibear.It is good to see some of Ideal's stock.Yes the sun does lighten buff,but since one is darker than the other, I am thinking she must have been lighter to start with. Years ago some buff breeders would select the darker hens and cocks that molted in new feathers and kept there color,rather than those that got lighter.It was a slow process but over many generations they developed a "stay buff" line that faded very little. Thin feathers are narrow rough looking feathers,select wide feathers in the breeding pen.Also some birds have spread tails where the feathers are wide apart most of the time,another thing to select for if you are breeding Buff Leghorns..