DIAGNOSIS This is a color calibration issue. The printer's understanding of color balance has drifted, often after a cartridge change, head cleaning, or just over time. It's not a clog, it's a software/alignment problem.
FIX You need to run the automatic color calibration. On the printer's control panel, press the 'Settings' button. Navigate to Maintenance > Adjustment > Color Calibration. The printer will print a test page, scan it, and adjust itself. Make sure you use plain white paper and place the printed page face-down on the scanner glass exactly as instructed on the screen.
IF THAT DIDN'T WORK If the colors are still wildly off, perform a 'Print Head Alignment' from the same Maintenance menu. This aligns the physical positions of the color dots. Run both the automatic and, if prompted, alignment for the best results.
HEADS UP For the calibration to work, the scanner glass must be spotlessly clean. Any smudge or dust on the glass where it scans the calibration page will be interpreted as part of the print, leading to incorrect adjustments.