Genuine OEM HP PSC 1350 Ink and Supplies
The PSC 1350's HP 56/57 combo includes black and tri-color ink. An HP 56 black twin or HP 57 tri-color twin instead gives you two of the same cartridge, so a twin isn't a black-and-color set.
Toner Buzz carries genuine HP 56 black, HP 57 tri-color and HP 58 photo ink, with singles, black and tri-color twins, and the 56/57 combo. Use a single for one ink type or the combo when you need black and tri-color together.