This was set as the new default as a huge number of top players use forced keel/bright with green settings to play.
You can disable it in the menu as described in the quote below, or with \clearcvar cg_forceEnemyModel if you know how to use the console. (if you don't check the guide in my sig)
As of the QLPP13 update Premium and Pro users can also use \clearcvar cg_forceEnemyModel, then \cg_forceEnemySkin bright
to have all the different models in use, but bright skins on them for which the colours can be chosen.
For more information on the coloured skin system in quakelive please see Ultimate Quake Live Guide post 6
(The following posts are from the original thread.)