Keying - Nuke 101: Professional Compositing and Visual Effects - page 314

18. Make sure you are viewing the RGB channels of Merge1 in the Viewer.
Notice the green coloration of the hair on the left—you will remove this. You can
get rid of it by using the Red Weight and Blue/Green Weight properties ( FIGURE
7.21 ) .
Figure 7.21. This green can be removed with the Weight properties.
19. While looking at your screen, adjust the Red Weight and Blue/Green Weight
properties until you get rid of the green color in the hair. Don't go too far or you
willcompromisethedensityoftheinsideofyourmatte.Iendedupwith0.455for
the Red Weight and 0.47 for the Blue/Green Weight.
To get a little more hair detail, check the Luminance Match box and then move
the slider a little.
20. View the alpha channel in the Viewer.