Comment 4 for bug 409353

I don't think your screenshot got attached, but no worries. I ran the test as well. Yes, byobu does in fact support the 256 colors, and when sending them to an Xterm that can do 256 colors they are displayed. That isn't where the problem lies.

The problem occurs when running ncurses app within screen with the 8 Color terminfo. ncurses apps look up the value in the terminfo database and sets its output from that. A specific example is vim.

When the term is set to one that only supports 8 colors, that is all vim sees.
:echo &t_Co in vim returns 8.

When you set TERM=screen-256color-bce then vim will see that it can output 256 colors by way of the terminfo database.
:echo &t_Co in vim will now return 256.

Here are a couple of 256 color schemes for vim. You will never want to use 8 color vim again. :)

http://www.vim.org/scripts/script.php?script_id=1243 - 256 colro desert theme
http://www.vim.org/scripts/script.php?script_id=1143 - inpot