Yeah create a box that fills the screen. Fill it with a very dark blue and set it to multiply (effects). Set object opacity to around 80% (depends how dark the box colour is, and how dark you want the scene). I highly doubt you can do this without effects, unless you draw everything manually.
Well, this might be the best method, although WebGl might be a luxury on some platforms. Thanks.
Just add an extra layer on top of your game's layers, make it it black, none transparent, and play with opacity.
I use this method in a day/night cycle system.
Thanks. Safest method, although I believe you lose some contrast with this. But with careful use it could be it.
Will try both.