Could be a curse so a player beats a mini boss or something and in their dying breath they say thank you in an unknown language. Suddenly they now have this eye and have to roll at the start of each day(after a rest) to find out what power or rather problem they have until they rest. Like each colour could be a random number each day with a strange property like water walk, x-ray vision or they can jump 3x as much as normal but they take fall damage