HP Color LaserJet 8550 Multifunction Printer series - Manual (Page 174)

174 Chapter 5 Image manipulation
EN
Negative/positive (Nega/Posi)
Negative/positive mode (which is listed on the touch panel display as
“Nega/Posi”) allows you to make negative images on copies by
reversing the color hues and gradations of the original. The copy
module uses complementary colors in the Nega/Posi mode.
Complementary colors work together to produce the same richness in
hue on the copied page as everyday objects have in direct sunlight.
Nega/Posi mode reverses these colors to produce a copy that
resembles a negative from a roll of film.
Below is an example of the copied output using Nega/Posi mode.
Figure 42 Color hues and gradations are reversed in Nega/Posi mode
Original Copy