Haha!
The colour is almost definitely due to the coin being in the ground for many years before it was recovered by somebody. Possibly with a metal detector

I would also bet on it having been through a rock tumbler.
Metal detecting in Australia can be quite lucrative with our 1 and 2 dollar coins being a big part of our day to day currency. many pockets have holes in them and recovering $100.00 or more in an outing is more common than you would believe. Can't wait for $5.00 coins

Some detectorists I know just dump all their coins in a jar when they get home and when the jar is full, or the bills are due, they do put them through the rock tumbler, bag them up and take them to the bank.
Our banks can be a little funny with dirty coins, and will sometimes make you go through a damaged currency process which could result in it taking some time before you get credited for your coins.