For my ambient light idea, I was able to fake it in X10 for a game I worked on for a while but never finished because of all the problems X10 had at the time. I did it by raising the water level all the way and then adjusting the water color and bloom settings. It worked really well, except for the fact that the everything was actually underwater and so the player could move/swim in all directions, defeating the purpose of having to face the enemies I'd made (see picture).
(by the way Daniel Wright 2311, I meant that it should have been included with FPSC X10 from the beginning, not as a criticism of the mod)
While I'm at it, I may as well suggest another feature. Not crucial so it can wait until other more important things are implemented but I'd suggest some sort of Material Editor or System.
As it is right now, FPSC X10 is very inefficient when it comes to textures. To make a simple color variation of a texture, rather than the engine just taking the existing texture and applying the variation to it (and then you being able to drag/drop the material on whatever you want), you currently have to fire up photoshop, make the variation and then save it as a new texture which takes up more space AND modify the .fpe or .fps file so it uses the new texture.
In other engines (like say Unity..) you make one texture and without ever leaving the editor you can make any number of color variations without leaving the editor. Also, a material file takes up only like 1kb or something like that, vs a couple mb for a new texture. For the memory one texture takes up, you could have hundreds of different materials. It also makes things like swapping textures a lot easier and stuff like that. Course such a system in X10 would probably be a lot of work, but it'd have a big payoff (especially since as far as customizing you game goes, the main thing in FPSC and X10 is custom media)
http://s140.photobucket.com/albums/r33/Sanky_Panky/Gabriel%20Acosta%20Unity%20FPS/?albumview=slideshow
My Unity FPS WIP