Keylight: Color Me Corrected

After you've knocked out the background, you'll usually need to adjust the foreground colors so that they match the colors of the new background plate. Keylight has two groups of color-adjustment parameters: Foreground Color Correction and Edge Color Correction.

"Foreground" means the majority (everything except the edge) of the person or object left behind after Keylight has removed the background.
"Edge" refers to a thin band of pixels around a person or object. Edge pixels often require special treatment because (a) they will usually contain the majority of spill from the knocked out background, and (b) they are the pixels that will be touching the composited pixels in the new background, so they're very important when you're trying to create a believable blend between foreground and background images.
To adjust how thick a band Keylight "thinks" of as the edge, adjust the Edge Grow parameter while displaying the Color Correction Edges view.