If you look closely enough at something, you will always find differences and flaws.
Stare at your skin long enough and you may see freckles and blemishes that you have never seen before and once you have seen them, you cannot unsee them.
It is very unusual to have symmetry in your face, that includes your eyes and eye colour, it is very common for one eye to be slightly different from the other, you may only notice this when looking closely in the mirror or may only notice it once someone has mentioned it.
This has nothing to do with anything you have done, this is something that has most probably always been there, it is only now that you are noticing it.
However, any extreme and sudden changes in eye colour should be brought to the attention of a doctor, as it can be a symptom of deeper medical problems.