Hi Dave:

Good question? All that I can say for sure is that I have never seen sun BLEACHED wood that got darker from exposure to UV radiation!

I have seen wood that has been in direct sunlight and wood on the same structure that was in the shade and the exposed wood was always darker than the wood that was in the shade!

Of course I am just a PFC who is quite ignorant in many things so take this information with a grain of salt!

Good luck with your question.

Franchi