Wow - how long does it take for a GHO to develop a color matching their environment?
Superbowl
For owls that are superb.
It seems to be a speciation based on what is more effective coloration based on their environment and foliage types. That wiki entry goes into the types of speciation, which is something I haven't read about before. It seems there are 4 types based on how far they diverge and get isolated from the original species.
This article I found goes more specifically into the GHO specific color divergences. As a heads up warning, there are non-living museum specimens as most of the example photos in the article. They are pretty good ones as far as preserved birds go, but they are very obviously inanimate now if that is something you don't wish to see.
I've seemingly got some type of eye infection so I can't really read either article now, but they both look good, and I'll have to come back to them myself.