The HP Officejet Pro 8600 Plus is identifiable by its model number: N911g. Released in 2011, the printer can be identified by its brown finish and touchscreen control panel.
Get into your printer settings and run the "Clean Print Heads" option (or similar wording). I used to get that when I didn't print regularly and the color heads would get clogged up, similar to an old spray paint nozzle.