The Surgeon General's Report on Purple Potatoes

That colour isn't dye and it isn't a trick of the light. Russian Blues are packed with anthocyanins, the same family of pigments that makes blueberries blue, red cabbage purple and blackberries stain your shirt.

Plants make anthocyanins partly as a kind of sunscreen and stress shield. In our bodies they behave as antioxidants, which is the reason nutrition folks get excited about deeply coloured fruit and veg. A regular white potato has almost none; a purple-fleshed one carries them all the way through, so every bite gets a share.

Before we even get to the purple, potatoes have been getting a bad rap they don't deserve. Eat one with the skin on and you're getting:

• Potassium, more than a medium banana, which helps keep blood pressure in check
• Vitamin C, roughly a third of what you need in a day
• Vitamin B6 and a useful amount of fibre (most of it in and just under the skin)
• No fat, no cholesterol, until we get involved with the butter

The purple varieties bring all of that, plus the anthocyanins on top.

Researchers have started looking at purple potatoes specifically. In one small, widely reported study, people with high blood pressure who ate a few microwaved purple potatoes twice a day for a month saw their blood pressure come down a little, without gaining weight. Other studies suggest purple potatoes may raise blood sugar a little less sharply than white ones.

These are early, small studies, and a potato is not a prescription. But the direction is encouraging, and "eat more colourful vegetables" is advice nobody has ever regretted following.

Anthocyanins change colour depending on how acidic their surroundings are. That's why a squeeze of lemon makes purple potatoes look pinker and a pinch of baking soda can push them towards blue-green. It's harmless, it's chemistry, and it's the best party trick in the produce aisle.