Following my previous question: What color does the other cone in Tetrachromacy correspond to?
People with normal color vision posses 3 cones in their eye. But there are some rare cases when people can have 4 cones (Tetrachromacy). These people, some of them will notice the shades difference in the scene through their eye. And the rest won't notice it, because simply their 4th cone is activated in the close peak value with the the L-cone. Therefore eye will not find any difference and will encode only one color even if it's coming from 2 cones stimuli.
How do you check, to know how many cones you have in your eye ? If the case is, even people who posses 4 cones can't even notice the shades difference ?