The HP No. 350 and No. 351 combo pack contains one of each black and colour ink cartridges. This printer ink package is compatible with a huge number of HP’s most popular printers from Deskjets to Photosmarts. The HP No. 350 is a straightforward black ink cartridge like any other but the HP No. 351 colour ink is a bit more complex. In the tricolour printer ink cartridges from HP there are all three colours (Cyan, Magenta and Yellow) which makes them wonderfully easy to replace and recycle.