It could mean a number of things. First things you would want to check your drum and toner cartridges to assure they're working properly. After that its either the drivers going into your printer or the connection itself is causing a signal interference. You should drive rolling your drivers for your printer.
1) Try turning the printer off and then turn it back on. 2) See if you can do a self-test (usually found by going through the buttons on the printer)
3) Try replacing the toner cartridge
4) Could be an ssue with the printer driver. Try reinstalling the correct driver (based on make and model) download from the manufacture's website.
The color ink tanks are most likely empty. Try replacing the ink tanks one at a time to find the empty tank. If this does not solve the problem, try cleaning the heads. The head cleaner is in the utility menu for the printer. After the head cleaning is complete, print a test page.
If it's a laserjet printer, chances are the toner has gone bad. Replace the toner and try again. If still black, it may be a bad fuser or other mechanical issue.