Keying - Nuke 101: Professional Compositing and Visual Effects - page 306

The other curve controls the amount of saturation, which can be edited in the
same way. However, it has little effect in this case, so you don't need it.
7. Click the point in the graph that's at X = 2, Y = 0 ( FIGURE 7.9 ) .
Figure 7.9. Clicking a point in the graph allows you to numerically edit it.
8. Double-click the X value next to the point itself. This displays an input field.
9. Change the value from 2 to 1.5, which will tell the keyer not to key out the hair.
Press Enter/Return ( FIGURE 7.10 ) .
Figure 7.10. Changing a point on a graph numerically using the input field.