We often discuss colour management and how using a calibration device on our monitors lets us create a set 'standard', whereby our photos should look the same on every screen that has been calibrated. Whilst this might be the case and work in theory, our eyes can be the weakest link in this chain. Some people are colour-blind and cannot differentiate between some colours/shades. Othertimes, though we might not be colour-blind, our eyes can play tricks on us.
It certainly does make you wonder if the way you 'see' a photo on screen, no matter how much calibration etc is done, if you are seeing what others see.