Piet is an esoteric programming language in which programs look like abstract paintings. It uses 20 colors, of which 18 are related cyclically through a lightness cycle and a hue cycle. A single stack is used for data storage, together with some unusual operations.
Piet was invented by David Morgan-Mar and is named after geometric abstract art pioneer Piet Mondrian.
If the stack is allowed to hold any arbitrarily long number then it's very likely Turing-complete. There's no formal proof though.