A colour is missing entirely
Run the nozzle check. If a whole colour block is blank, that channel is either empty or blocked. Take the cartridge out, check the orange tape is off and the contacts are clean, and reseat it until it clicks. On a printer that's sat unused for weeks, a fully dried channel sometimes needs a deep clean and a night switched off before it comes back. On MegaTank models there are no cartridges to reseat, so a dead channel points at the print head instead.