Even though my black cartridge is full, my black and white documents are so light they are unreadable. My color cartridges are close to being empty. Can this be the cause?

Similar to the first answer above, unless you select the default printing choice to use black ink only you will be using all colors, even to print black text in a document.

Wether your printer uses one color cartridge or multiple color cartridges, all the colors are mixed together to get black. I bet your blue cartridge is the lowest?

You need to make certain you select black only, or select to have color printing off.

Also, to save a bit more ink you can select, as a default, for all documents printed to be in draft mode (only good if most of your printing is for yourself-not for "real" printing of letters, correspondence, reports, etc.).

Even when you make the default black only and draft, when you change settings to print a picture or a "real" document you MUST remember to change it back.
I forgot not too long ago, and now all my colors are low!

Printers use all cartridges to get the correct colour even black
best get a new colour cartridge then realign the printer with a test pattern

Run "print head cleaning" in the printer maintenance menu. Run head cleaning about 5 times. No need to run deep cycle just normal head cleaning. if solved please visit my website http://besthealthdeal.five-starsports.com/home.html