got no idea no idea what this is it looks like some of them tone coins that they give mint State 69 grades too on one side and then the other side is perfect very much so like this coin anyways it's probably just nothing thank you for looking
If I am not mistaken, MS grades are given according to how many little nicks or other defects are visible on an otherwise uncirculated coin (and other factors in the highest states, such as strike quality). Usually tone is not considered. It is not the tone that makes the grade, but the grade in spite of tone. Some collectors pay a premium for what they consider beautiful toning. Personally I don't like any toning, but that is a good way to start an argument. Anyway, as Collecting Nut said, your coin is not a high grade and the "toning" or "environmental damage" doesn't help it. Easily worth 10 cents, however.
I was told that toning eliminates a few of the bad scratches or Nicks depending on where they are on the coin and things like that
My personal opinion post mint damage that's not what the coin comes out of the mint looking like so it's supposed to be damaged just like any other coin that has a mark on it it would be post meant damage that's my opinion
There are various detractors that take away from a coins grade. Natural toning is generally not a major detractor...but can be. Nicks and dings in one area versus another will also modify the grade assigned. For example, a 2 mm ding in an obscure location on the field vs by the nose or on it will generally rate less significant and affect the grade less (also, obverse vs reverse can play a factor). This plays out in the numbers of graded coins that you can find online at the various grading sites where two coins grading the same, but one looks 'busier' with dings and blemishes than the other. However, a similar study on clean coins and naturally toned coins will indicate that the delta between them is less significant.
