The Canon 790 is a printer model that typically uses Canon ink cartridges. For specific ink compatibility, it's best to refer to the printer's manual or Canon's official website. You can also check the ink cartridge numbers compatible with your printer model, usually found on the cartridge itself or in the printer documentation. Once you have the cartridge number, you can search for compatible ink colors, including blue, from Canon or third-party ink suppliers. Always ensure compatibility to avoid damaging your printer or getting poor-quality prints.