I've noticed that before too, but I think I figured it out, and the answer is adriandavidb's response.
I made a batch of Blade1212's tikka yesterday, and accidently poured way too much food colouring into the marinade. Probably just under a teaspoon. I only marinated the chicken for three hours before barbequing, but the end colour result was very deeply pentrated into the chicken. Mystery solved.
Downside is that my hands are STILL orange.

-- Josh