Sorry, I'm behind in my reading, just came across this thread.
Most likely is that he'd recently molted and his colors were still
'bright' from being newly exposed. Many snakes are captured just prior
to or after molting (or during, for that matter), as they are somewhat
sluggish for ~48 hours before and after the molt, making them less alert
and slower to move off when stimulated, and less able to resist capture.
But, having had many snakes in my time, they all lose a bit of color
when captive. Not sure about why. Stress? Diet? No clue.
I had a hognose snake when I was a kid for several years, missing part
of her tail. Finally I let her go (not enough cages) and she hung
around the hog barn for a couple of years before she disappeared. What
I noticed about that was that her colors were brighter when she was
"free" than they had been all the time I'd had her captive. After a
molt when captive, the colors were improved, but after a molt when free
she was almost pretty for a week or so--not had hognoses are really
pretty snakes; they're rather blah greys/browns/tawny and not striking
at their best.
What is a beautiful creature is a blue racer just after the molt.
Absolutely riveting. They make lousy pets, though. Darned things bite
forever, never get used to people.
Susan Jane, on the blazingly beautiful Maine coast.