A colour has stopped on a separate-printhead model
Here the printhead is a separate part that outlives many cartridges, so a dead colour means either an empty cartridge or a blocked channel in the head. Check the cartridge is genuinely seated and not just sitting in place, then run one cleaning cycle and a diagnostic page. If the channel is still dead after two cycles, leaving the printer switched off overnight sometimes softens dried ink in a way repeated cleaning won't. A printhead that stays blocked after that is a replaceable part on some models and a service job on others.