Greetings
I would be more than happy to help you with this print quality issue you are describing.
Are you using Genuine HP ink cartridges?HP recommends that you use genuine HP ink cartridges. HP cannot guarantee the quality or reliability of non-HP ink cartridges or refilled HP ink cartridges. If you do not use genuine HP ink cartridges, the steps in this post might not resolve the issue you experiencing. You could also see how non-HP supplies compare to refilled or remanufactured cartridges from the Buyers Lab Report.
Have you tried all of the steps listed for Fixing Print Quality Problems for the HP Officejet Pro L Series?
You could also look into getting a new Cyan/Magenta Printhead. You should be able to find one using the HP SureSupply website.
Please let me know if any of these steps resolved your issue, or if there is anything else I can do to help.
Thanks,