Printer has coloured ink but no black ink and wont print out in colour?

With most printers, you are required and need to have ink in both the black and color ink cartridges in order to print in black as color ink is needed in this process. They work in conjunction with each other. So you will need to have the both usable color and black ink cartridges with ink and are not low, the same thing applies for color. The ink acts as a lubricant for the print heads (water not oil) to help prevent print head clogging. Some color ink is used even if you only print in black or vice versa. If you printed with a empty color cartridge it can damage and clog a printer's print heads. At best you'll have to replace the cartridge and do some maintenance; but you could end up damaging the print head so badly you'll need to replace it.

black is also used as a color when printing...