Watchmaker Richard Mille is known for pushing the limits — of engineering, design and price — selling the world's most expensive watches with an average retail price of $185,000.

But now Mille has reached a new extreme. It's a piece of graffiti made for your wrist, priced at $800,000. And it's already sold out.

The watch is called the 68-01, and it's a collaboration with the famed French graffiti artist Cyril Phan, also known as "Kongo." The artist is used to working on a giant scale, painting bridges, walls and vans with his famous bright colors and cartoonish tag. For the 68-01, he had to paint each of the hundreds of tiny parts inside a tourbillon watch the size of a postage stamp.

It took more than a year just to develop the paint and special airbrushes used to color the parts, since the paint had to be thin and light enough not to inhibit the microscopic movements.

"I wanted to create a cultural shock, a shock between two different universes," Mille told CNBC at his lab in Switzerland. "He's always doing very big pieces and we are doing very small. It's the shock between the artistic world and the technical world. It's the best of technique and the best of art."

When they first discussed the idea, Phan proposed just painting the face of the watch. Mille rejected the idea, directing him to paint all of the internal parts, which are visible through the watch crystal. Since many of the parts move, the colors also change throughout the day.

"When they are turning the scenery is changing. The design is never the same. But it has to be a message — so there is a mixture of colors but there is also the artist message in each watch."