Chinese customers at McDonald’s have been baffled by the latest item to hit the menu.

The Modern China Burger, which is only available until November 3, comes with a speckled grey bun that some have compared to a rock.

The burger itself consists of two pork patties, bacon and salad topped with spicy Sichuan pepper ketchup – a kind of burger version of pork bao. But the bun has been attracting attention for its sickly grey colour. It is made with steamed mantou, a cloud-like steamed bread popular in Northern China that is used to make steamed buns.

Coloured burger buns have become popular in recent months as fast food restaurants try limited runs of food to set themselves apart from the competition. Burger King’s all-black Halloween burger backfired, so to speak, when it was discovered to have unfortunate side effects.

A photo posted by Thomas Bailey (@trbailey_2) on Sep 29, 2015 at 9:25pm PDT

McDonald’s Modern China Burger may be too late to rescue the chain from falling sales that have led some US franchise owners to claim that it is in a “deep depression” and facing its “final days”.