Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
Lets start with a deep cleaning of the printheads.. The link below explains how to do that using a mac
Then, try a test print once thats finished. If its still printing dark, let me know and we may need to reinstall the driver or change some of the print settings.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.