Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 129

Figure 3.43. Close the Color Wheel and Color Sliders panel with the top left
X button.
7. Ctrl/Cmd-click the Viewer to remove the red sampling box.
This made the rim part of the fur look more like part of the fur. Doing this to
the fur using only the beauty pass would have been immensely difficult ( FIGURE
3.44 ) .
Figure 3.44. Your changes should create an image similar to this.