The battle between the world’s blackest black and the world’s pinkest pink, and between the two artists associated with those colors, reached a new height today, just in time for Christmas.

Artist Anish Kapoor has sent a salty reply to Stuart Semple, the British artist who has taunted him over his having secured the sole rights to use Vantablack, the world’s darkest pigment; many artists responded with indignation to the exclusive deal.

Semple offers a tongue-in-cheek product that he calls the world’s pinkest pink, which he makes available on his website to any buyer but Kapoor.

In an Instagram post, Kapoor has coated his middle finger in the pinkest pink, a jar of which sits open near the gesturing hand, with a caption reading “Up yours.” In just a few hours, the image has garnered upward of 500 likes.

Up yours #pink A post shared by Anish Kapoor (@dirty_corner) on Dec 23, 2016 at 2:32am PST

Kapoor or one of his agents has, it’s worth noting, violated the terms of service put forth on Semple’s website, and Semple isn’t happy. He expressed his deep concern over the situation in an email to artnet News:

We are all extremely disappointed to see that Anish Kapoor has illegally acquired the world’s pinkest pink. He’s walked into this paint war with a gesture that cannot be misconstrued. He’s given the art community a bright pink middle finger. He is still very much at large. Not only has he refused to share the black, he’s now stolen our pink. Rest assured, we will get to the bottom of who has purchased this on Anish Kapoor’s behalf and broken their contractual agreement with culturehustle.com, and we will instruct our lawyers to take appropriate action against such breaches. We are pleased to note that he has not managed to get his hands on the World’s Glitteriest Glitter—yet—and we urge purchasers not to share the product with Kapoor or his associates.

It’s shaping up to be the nastiest artist feud since performance art legend Marina Abramović accused rapper Jay Z of betrayal over his failure to make a donation to her foundation … before Hova produced the receipt for same.

Kapoor did not immediately respond to a question from artnet News, posed as a comment on his Instagram post, about how he managed to acquire the pigment. We’ll update this story as events warrant.

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