Actually, there's quite a bit of greenish/aquamarine-tinted stuff in and around the gateroom. I suspect that it looks like lighting on-screen, but quite a bit of it is actually paint, and darker than you'd think under regular lighting, since it gets washed out a lot when they light for filming.

The practical wormhole effect (as opposed to the CGI effect) casts a faint royal-blue light over everything, as it's essentially a ginormous light with a blue gel over it.

(Not that I'm all bouncy about having been on a set tour, nor horribly excited about going again in March. *koff*)