Grimace would approve of these eye-catching dessert drinks made with one of Japan’s favorite seasonal foods.

It was only a week ago that McDonald’s Japan introduced its new lineup of extra-matcha green tea dessert drinks. In the fast-paced world of Japanese sweets, though, you’ve always got to be getting ready for the next flavor, and, in this case, the next color.

So while the green tea items remain on the menu, they’ll soon be joined by purple McShakes. In the past, McDonald’s Japan has offered such fruity shake flavors as white peach and Hokkaido melon, which might have you thinking these are grape concoctions, but the star ingredient is something else entirely.

The new McShake is actually flavored with murasaki imo (literally “purple potato”), a type of Japanese sweet potato with a vibrant violet hue.

Murasaki imo are at their most delicious in autumn, which is why McDonald’s is unveiling the drink now (plus decorating the bottom of the cup with autumn leaves). As an added bit of seasonal appeal, it won’t be long until Halloween, a celebration Japan has embraced in a big way over the past few years and is locally associated with the color purple, like with the purple chocolate French fry sauce, purple pancakes, and purple potato salad we’ve seen in years past.

The Murasaki Imo McShakes are priced at 120 yen (US$1.10) for a small and 200 yen for a medium. They’re scheduled to go on sale September 26 and will be available for a limited but unspecified time, but there’ll be at least a bit of overlap that’ll let you drink them on the same day as Starbucks’ crispy sweet potato Frappuccinos.

Source: McDonald’s via Japaaan
Top image: McDonald’s