In the image below that I just took of my peppermint plant you can see that the leafs have this silver-grayish spots that don't look healthy. What am I doing wrong? Is it too much sun maybe?
Mint usually does not mind a lot of sun provided there is water to go with it, otherwise it can dry out quite fast if it is not deeply rooting. As to your leaf issues, I think maybe there are two possibilities: some of the leaves are showing a kind of salt-shake spotting of the leaf, and one or two of the large leaves are possibly showing tunnels. The first damage is typical of leaf hoppers; they jump to the leaf, bite, suck and jump again. So the result is a lot of closely spaced spots where the leaf has been damaged. The big leaf towards the centre of the image shows what looks like a continuous line along one of the subordinate veins; examine this closely and see if it might be a leaf miner. In both cases you should be able to find a culprit in the act of chewing the leaf. Once you can make a positive identification you can move on to what measures to take against the damage. You can find further info and countermeasures on the leafhoppers here from the University of Connecticut IPM Program.