This floor is solid 3/4" walnut with no stain, just clear polyurethane.

Our floors looked like this when we had our home built 7 years ago. Beautiful and I loved them! We have a lot of windows (with a covered patio and uv windows) and unfortunately our floors have still faded very badly and turned an "orange'" color. Not the look I was going for and am now stuck with it.

could it be the urethane that yellowed and not the wood? Perhaps they just need refinishing with a something more UV stable?

My floor is 3/4" solid walnut. No stain, it was sealed and finished with Bona floor finish. Thanks for the advice, maybe some day we will have them refinished. They still have a good finish on them but I didn't know about checking for UV stability. The flooring under the rugs is a much different color now than the rest of floor. It doesn't appear to be the Bona since the the area that gets the most sun is almost all the same "orangish" color now. The former brown areas have lightened considerably so there isn't a lot of variation in the planks anymore.