Here is a the link to a search I did for "hard" facts for you. I read at least 10 or 12 of them, but couldn't find any "official" or definitive word on it.
My understanding is that color is more connected to what fab plant the chip was made in. Also, that AMD was supposed to be moving all their chips ( at least XP's and Bartons ) to green. None of this can be confirmed.
I just opened the drawer next to me. I have three TBreds in there. One week 10 ( 0310 ); it is brown. 2 week 19 ( 0319 ) >> they're both green.
Who knows? For all intents and purposes, the color doesn't matter. That has been my experience, and I have at least 10 TBreds running here.
oh yeah, the link. read for yourself:
http://www.google.com/search?q=AMD+%...&start=20&sa=N