The last time I shot a green screen with my C300, I was having trouble getting my bright green green screen to actually look green on my 17" monitor. It looked more aqua or teal. I tried a few picture profiles and I settled on OFF. I ended up lighting the screen tungsten and the subjects daylight and used the daylight preset WB. (weird, but it worked). Is this some a problem with Canons? Occasionally they do give me some weird colors. Maybe its how the camera sees my particular green screen (a sort of a fuzzy latex material)? I have another green screen shoot this week and I'm wondering if I should just bring my EX3 instead, but I want to give the client the better recording quality. Any thoughts, ideas, experiences, solutions?...

Have you tried adding green gels to the lights you are using to light the screen?

And put some 1/4 minusgreen on your back and edge lights

Also, are you able to check things out with a scope? I've become a big fan of ScopeBox (using the BMD mini-recorder as a thunderbolt adapter.)

What Dave said, and...

I think some of Canon's stock profiles are aimed at different renderings of caucasian skin tones, and skew towards the warm, some towards the warm and Magenta.

Magenta is opposite the color wheel from Green, so, it isn't surprising that a profile that works opposite will have some significant affect on Green.

A pure color in the screen and minimum spill is more important that a pure green color. With most of the current keying tools you'll be specing the key color anyways. It's certainly not going to hurt to light the screen tungsten and foreground daylight, but it may not be helping!

My favorite green screen tricks are much like Dave's: Lighting with green Kino-flo bulbs, cheating back/rim lights towards the Magenta (that's minus-green! Green + magenta = white), checking the screen on waveform monitor for eveness, and on vectorscope for color purity, good subject-to-screen distance to control spill...

I've heard various approaches on screen luma intensity. Some insist that the screen should come up to 70-IRE when the subject is properly exposed. I'm usually a little lower than that. I have had screen color issues that have been tamed by bringing more light to the screen. I try to keep the screen north of 60-IRE.

Canon Log definitely does some weird things to blues and greens. I would probably stick with a standard rec709-based profile for green screen work, like normal 1-4 gamma and color matrix.