Toned coins are a very specialized section of collecting. Toning most commonly occurs on silver and copper coins. Gold coins are the least likely to tone, although they sometimes do due to the small amount of copper in US gold coin's alloy. Toning begins when the coin's surface comes into contact my oxygen or sulfur. Moisture, heat, and other outside factors can cause coins to tone as well. Morgan Dollars are widely collected for their vivid colors, along with other popular series such as Lincoln cents (looking at you, @CentSearcher). The reason a lot of Morgan Dollars have very special toning is that the cotton that made up the bags the coins were stored in during their time at the vault produced a chemical that, when in contact with the surface of the coins, created some lovely shades of color. 
This week's Toner Tuesday (or Wednesday, I guess) I don't own, but I have been shadowing the coin for a long time. Once I get a job, I will track down the owner, and tell them to name their price. The coin I am talking about is this 1881-S PCGS MS-63 Morgan Dollar with lovely hues gracing the upper obverse. It rightfully earned its "green bean" CAC sticker with its mesmerizing blue, red, and orange surfaces. It went for $475 on eBay in 2018. I would love to own this coin one day, and if you know the owner, please put me in contact with them. 
Keep collecting (and looking at this awesome coin), Thatcoinguy
P. S. If you want to use the #tonertuesday for your posts, I certainly won't stop you!