This is called “spill”, and it occurs when you subject is too close to your screen, both Ultimatte and Keylight generally deal with this automatically.
But it your case all you may need to do is manually balance your white and black points. No keyer is going to give you perfect results right off the bat, you’ll need to tweak the spill-balance and base-matte settings until something looks good.
I’ve used many choma-key plugins for ae including Ultimatte and Keylight, but i prefer dvmatte by dvgarage (especially if your footage was scanned to DV)