Fogging.
How about an option in project settings like depth of field except that objects are tinted with a user definable colour as they get further from the camera.
a lot of 3d apps have this and it is used to great affect.
Wow, that would be a very cool effect indeed! Good idea! I could use it a lot! This could bring all sorts of 'moods' into your scenes, if you understand what I mean (my English is not that well).
Off course, maybe, you can also make something like this effect by hand now, using layers with colours overlaying with alpha... But it is tricky to do it that way maybe (I'm just learning Moho so I don't really know the program well enough yet), because if you zoom into your scene with the camera, you have to tween all those layers. It would be great if this was a standard feature.