It's an 1824 Bust Half Dollar, O-109 with a rarity of 2. Both sides contain colorful toning with rainbow like colors.
It's been cleaned and polished, and retoned (possibly with assistance). The marks in the obverse left field also look like whizzing.
You can see marks around the rim on the reverse that makes me think it was mounted on a type of coin bezel or piece of jewelry like a lapel pin or even maybe a money clip. See the 3 marks? Evenly spaced out? Like notches. The color could be a lamination residue like varnish to shine it up.
If it was a jewelry piece and that seems logical with the evidence Paddy presented, then this coin likely was cleaned many times with all different kinds of chemicals. That could be a factor in the toning.