British artist Stuart Semple just came out with a dazzling pair of new paints that change color when they're heated up. And anyone can buy them for $27 to $31 apiece ... as long as you’re not Semple’s fellow artist Anish Kapoor. Thanks to a protracted battle over the use of a very special black color, Kapoor is legally forbidden from buying the paint, according to Vice.

The move is only the latest battlefront in a year-long war between Semple and Kapoor over the rights of artists to monopolize certain colors.

In February 2016, Kapoor earned the ire of essentially the whole art world by buying the exclusive rights to Vantablack, known as the blackest black ever created. Keeping a complete monopoly on a new color was derided as selfish and immoral by Kapoor’s critics. Artist Stuart Semple was one of those outraged critics, and he has since retaliated in kind, developing multiple paints that he has forbidden Kapoor from using.

First, in November 2016, Semple created what he called “the world’s pinkest pink,” selling it on his website for dirt cheap—as long as buyers certified that they were not Anish Kapoor “who won’t share his black!,” as the website states. Then he created “the world’s most glittery glitter,” a super-sparkly glitter made from high-grade glass shards. To Semple’s dismay, Kapoor did get his hands on the world’s pinkest pink through the London gallery that represents him, giving the feud new fuel in the form of an Instagram of Kapoor’s middle finger covered in uber-pink paint powder.

And then came Black 2.0, Semple’s attempt to create an extremely dark black that would actually be available to artists, unlike Vantablack. That, too, is sold under the agreement that the purchaser is not Kapoor.

Now, Semple has come out with yet more awesome-looking paints that Kapoor is banned from using, which he says is a response to news reports that Kapoor’s studio extension in London will block out his neighbors’ natural light. Shift and Phaze are color-changing paints that respond to heat. Shift transforms from Black 2.0 to a rainbow color, and Phaze transforms from a color called Purple Haze to Pinkest Pink.

Like basically everything on his site, Semple’s latest products come with this addendum in his online store:

"By adding this product to your cart you confirm that you are not Anish Kapoor, you are in no way affiliated to Anish Kapoor, you are not purchasing this item on behalf of Anish Kapoor, or an associate of Anish Kapoor. To the best of your knowledge, information, and belief this material will not make its way into the hands of Anish Kapoor."

Even if Kapoor wasn’t planning on painting anything a transforming purple-pink, he probably wants to get his hands on this color. Both Phaze and Shift are incredibly fun to watch in action. If anything, this feud is only inspiring Semple to reach more creative heights. Regular artists may not be able to use Vantablack, but at least they’ve got some extremely fun alternatives.

[h/t Vice]