My printer's colour ink won't print properly. What should I do?

The 20 is the right cartridge. The colour cartridge is either empty (or close to it) or defective/plugged. You need to either get it refilled or buy a new one. You're using a remanufactured cartridge, you might need to find a better brand.

They are both the same cartridge your fine, does the colour cartridge have ink in it ? if you take a paper towel and fold it in half and dab the cartridge on it do you get three solid colours of ink ?, if you do have ink in the cartridge and it's not bleeding good just , boil some water, put about a quarter of an inch of water in a container and dip the cartridge in and out of the hot water a few times, then try it again on the paper towel, is it better ? if it is great try it in the printer, if it's not get the cartridge refilled.

First of all if you're not sure its the right cartridge you my hve just answered your own question.

It very well might be the cartridge is incorrect.

If not, then probably you need to prime the cartridge or clean the heads of the printer.

In which case that is done through the control panel. Click on the printers icon and choose service your printer.