We've been having problems with greenscreening. We thought we had a good result, but we really didn't look close enough. We're using an AE plugin; Keylight 1.2. Which is a great pice of software, that's been used for a zillion Hollywood films. Point being, it works just fine.
The main problem is always the same; we key out our green, but it also removes some pixels from our puppet, resulting in a hideous dancing grain. It's been frustrating, because it feels like we're doing everything right. We've been reading the instructions. And Dave has the photographer training. Switching the Keylight view to 'screen matte' shows us that we've got a clean result. Likwise with 'status view'. The only thing that killed the grain was switching to 'Intermediate view', which disables the spill suppression. So our problem is spill. But we put the puppet on a black base (instead of a green one); same result. The tiniest bit of reflection from the not-quite-matte black was giving us a teeny bit of spill, which meant grain. We figure we can disable the spill suppressor - doing so results in a bit of a green halo around the subject - and then clean up the rest with different keying tooks, choker mattes, etc. But we don't want to do it that way. The most recent shot took 20 minutes to animate. If it takes 45 minutes to key, that's an obvious problem. What we want is to pick our matte colour, and poof, have a passable result right away without touching a setting.
We tried using blue instead. It totally solved the problem. There was a teensy bit of grain in a test case wherein our foreground blue was very different from our background blue, and the foreground blue area was larger than it needed to be - we could have blocked it off to get a minimum of spill. But a proper test was totally fine. We like to do a few tests, to see where the threshold is for suckage. We're not toally sure why blue works so much better, but it does.