Anish Kapoor is banned from his rival’s art store.

A new art store opened this weekend in London’s posh Mayfair district, offering premium paints and pigments to anyone, except for world-renowned artist Anish Kapoor. A security guard equipped with a photo of Kapoor is posted at the shop’s door at all times to ensure he doesn’t get in. All shoppers are required to sign a disclaimer certifying that they are not affiliated with Kapoor or there to buy paint on his behalf.

The store, ArtShop, is the latest battleground in the color war between its creator, artist Stuart Semple, and Kapoor that began in 2016, when it was revealed that Kapoor had secured exclusive rights to artistic uses of Vantablack, the blackest synthetic material ever created. The fact that this new material with enormous artistic potential was only available to one artist incensed many in the artistic community, including Semple. In retaliation, he created a paint he dubbed the “Pinkest Pink” and made it available for anyone to buy online—except Anish Kapoor. The terms of purchase for Semple’s pink paint included the caveat:

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 paint will not make its way into that hands of Anish Kapoor.

But that didn’t stop Kapoor from getting his hands on the “Pinkest Pink.” He infamously posted a photo on Instagram of his middle finger dipped in a small pot of Semple’s paint, with the caption “Up yours #pink.”

Semple claimed his decision to have security on hand at all times to keep Kapoor out of his new art store was informed by that earlier defeat. In a press statement, he said: “Since the artist in question broke the legal terms of service on our website, acquired the pinkest pink and posted it on his Instagram, we’ve had to ensure security measures at the store are adequate to prevent a further breach.” His store not only offers the fluorescent pink hue that provoked Kapoor’s ire in 2016, but also Semple’s “Black 2.0” and “Black 3.0,” the latter of which he has claimed is the blackest black paint in the world.

For Semple, who continues to work as an artist, the store is more of a statement and an experiment than a move into the retail paint business. As he told It’s Nice That: “I wouldn’t say I’ve become a retailer, I’m still an artist. ArtShop is quite a conceptual work.”