Keying - Nuke 101: Professional Compositing and Visual Effects - page 310

The main things left to remove are the fine hair details around the edges of the
black patch. If you leave them there, you will actually be instructing the IBKG-
izmo to get rid of these colors, which is not what you want to do.
ThenextstepwillbeadjustingtheDarksandLightsproperties.Foragreenscreen
element, you adjust the G (green) property. For a bluescreen, adjust the B (blue)
property.
7. Click to the right of the 0 in the Darks G property ( FIGURE 7.14 ) .
Figure 7.14. Place the cursor to the right of the available digits.
To change really fine values, you'll need another decimal digit.
8. Enter .0 . That's a dot and then a 0 ( FIGURE 7.15 ) .
Figure 7.15. Using the arrow keys to nudge values is a convenient way to do
fine adjustments.