You say in your Question that "the printer cartridge picture shows that I am coming to the end of my print cartridges". I assume therefore that it will eventually change to say it is empty. (A common feature). If this happens, just change the empty cartridge (no need to change both unless both are empty). When my "picture" is getting low , I order what I need on line (you could go to a shop) so I am ready to change it when required. If you use a lot of ink, it is OK to keep a spare one of black and colour in preparation to change them, but it is not good to buy ink which will not be in use for several weeks. Usually, when a cartridge is empty, the printer will not function anyway. I dont know about your particular model so please excuse my general information.