Probably one of the colours hadn't got through to the nozzles and that affected the output. Some compatables recomend two or three cleaning cycles before actualy using for printing. WHSmiths do for example.
If you hesitate while installing Epson cartridges, it is possible to break the seal before the cartridge is properly seated. In these circumstances it is possible (just) that a few drops of ink my dribble into the wrong place. With you doing a cleaning procedure, this has cleared and everything is now OK.