These are your options copied from ttt.badking.net. Pick one, there is no “every color but green” option.
ttt_playercolor_mode (def. 1):
Sets player coloring mode. 0 = off, 1 = muted/dark colors only, 2 = select from a larger list of colors including brighter ones, 3 = fully random colors.
[editline]6th May 2014[/editline]
Also if you set it to 0 on the server it should also be 0 in game, make sure to change map if you ever update your server.cfg or autoexec.cfg