2015 D Dime Cleans Itself And Changes Colors On Me

Greetings, this is my first post here and I am new to the world of numismatic (And loving it! but going cross-eyed staring at all my coins lately). So forgive me as I am still learning the terminology.

So in layman's terms, I found a 2015 D Dime deep in a closet. Inspected it and thought it looked quite dirty with a faded brown/copper/light gold looking color all around it. Dropped it in a bowl of room temp water to wipe whatever I can. However, the dime turned nearly close to silver in a matter of seconds before even touching it. Picked the dime out the bowl and thought all that brown stuff on the coin would be floating in the water or at least make the water change color. But there was nothing. Water was still clear in color without any residue. Dime was close to all shiny silver for a few seconds out of the water then the brown thing slowly faded back onto the coin.

Sorry if I wasted your time reading my novel above if this post is irrelevant or if its in the wrong forum/topic. Just didn't want to leave out anything that might be important.

Pictures are:
1. How it looks when I'm not messing with it.
2. How it looks when I add room temperature water to it (Bottom streak of white is from camera flash).
3. How it looks with a light shining overhead directly at it.

Any thoughts?