Don't reach for the printer under your desk just yet, Printer Light in this instance refers to the old method of shining gelled light onto film to get a certain tint or white balance.
Command + Option + ` = Printer Light Hotkeys
The shortcut itself does not do anything, but instead engages the number keys to control the Offset part of the Primaries Wheels.
+ Red 7 - Red 4
+ Green 8 - Green 5
+ Blue 9 - Blue 6
+ Cyan 1 - Cyan -
+ Magenta 2 - Magenta 0
+ Master + - Master Enter (only works on num pad)
Using the number pad of a full size keyboard makes more logical sense than the number row on top of your laptop keyboard because the adjustments are made in + or - color pairs such as +7 and -4 to adjust the Red tint up and down. The number row keys still work as Printer Light Hotkeys as well mind you, just takes a little more time remember what key does what.
Available as a keyboard cover from kbcovers.com
I highly recommend a dedicated coloring interface like the DaVinci Resolve Micro Panel for a satisfying coloring experience (it does exist). But if you're on the plane or in the coffee shop with your laptop these shortcuts are very much prized time savers.
Finally, don't forget to disengage Printer Light Hotkeys (Cmd+Opt+`) to get your keyboard back to normal!