Re: i cant get a good Greenscreen key with an actor with red blood hair!!

There are a couple of ways to sort out haloing like this. Firstly I'd split your shot up so that the key you have pulled for the majority of the 3shot is one area of the comp, then have another comp tree that just deals with that guys head (use rotoshapes to set this up). The most simplest method is to work on the key just for his hair, then choke it. This is unfortunately often the ugliest solution, so you are more likely to get chatter and nobody likes crunching what were nicely keyed edge details.
The other way is more complex, it doesn't work all the time but in film work (where you're adding grain back in) it can work a treat, and is one of those tricks that seems to be a bit of a trade secret to those artists who do it (I was shown one technique based on this by someone but cannot pass it on step by step as they'd kill me, but I'll describe it here in general terms ;-)
The aim is to find a way of smearing the inner colour of the hair out along the edge (i.e. you want to place blurred colour from the hair over the edge region that has the halo), combining this with the original background, before using your earlier key, to act as an alpha for the foreground over the background. There are various ways of doing this, the main thing is getting the blend between the original hair and the new blurred out piece working, also this blurred out piece has to be wide enough to encompass the whole halo region (the edge itself doesn't matter as it will be defined by the key you're using as an alpha). The one tip I'll leave you with is remember that blurring functions, by their nature, bloom/spread colours outwards (but likewise, the more you do that, the more things get muddy). Goodluck, sorry I can't be more specific, but I hope this will get you thinking and experimenting.

Goodluck,

andrew