HP Color LaserJet 8550 Multifunction Printer series - Manual (Page 288)

288 Chapter 9 Maintenance and troubleshooting
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When the
REPLACE ** (COLOR) TONER
message appears, copying
is no longer possible. Replace the required toner color.
Figure 58 Toner cartridge message -
REPLACE ** (COLOR) TONER
If you notice changes in the color exposure of copy images after a
color toner cartridge has been replaced, perform Automatic Gradation
Adjustment to improve the quality of the copy images. For more
information, see “Automatic Gradation Adjustment” on page 277.