Correction: An earlier version of this story incorrectly said that alkaline soil leads to blue hydrangea blossoms that, in acid soil, would be pink. It is the opposite. This version has been corrected.


Not all blue foods enjoy the same popularity that blueberries do. (Barbara Damrosch)
Contributor

My mother, always very clear in her preferences, did not like blue food. I could understand that feeling. Wasn’t there something weird about the bright blue popsicles of the 1950s, oddly flavored with coconut? Or the swimming-pool blue of curaçao, an orange-flavored liqueur dyed with artificial food coloring to make it seem tropical? And what about blue M&M’s? Fifty-four years after the famous pelleted candies were created in 1941, blue ones were added to the merry mix. Why did we need those?

Blue foods sometimes seem unnatural because they raise suspicions of artificial, synthetic coloring, but there may be another reason as well. The color blue is rare in nature. Yes, Earth has its vast blue sky (and the vast oceans that reflect it), but only because of the way we perceive space through the Earth’s atmosphere, lit by the sun.

One could argue that the difference between looking blue and being blue is a fine point and that on some level all colors are a matter of perception, which varies according to the creature that perceives them. But there is still a difference between a solid lump of blue cobalt and the shimmering blue of a morpho butterfly’s wings, which is not produced by pigments but by microscopic structures that manipulate the angle of light to create a blue iridescence.

A few animals — a brilliant blue starfish, for one — do have blue pigmentation. The seabird named the blue-footed booby gets its foot color by eating certain blue-pigmented algae. But such species are so unusual that they would barely fill a toy boat, let alone an ark.

Blue eyes aren’t even blue. They just lack enough pigment to make them brown.

Blue color in plants is commonly caused by the antioxidant pigment anthocyanin, which is normally red or purple but can be modified — often by pH — to produce a truer blue. Acidic soil, for example, will lead to blue hydrangea blossoms that, in alkaline soil, might be pink. Red cabbage leaves can similarly edge into blue territory, although with many members of the cabbage family, such as kale or broccoli, a bluish tinge may result from the presence of “bloom” — a whitish, waxy protective covering. You can also find it on bluish leeks, such as Blue Solaise (which turn purplish in cold weather) and on some fruits, such as plums, that would be a deeper, more purple color without it.

Blueberries have this covering, too, adding to the fruit’s unusual blueness. Blueberries are one of the few blue foods that are widely accepted — though even they turn purple when cooked. They’ve been part of North American culture for a long time, unlike the more recently introduced purple corn and purple potatoes, both of them anthocyanin-rich. These have earned some popularity, but some find them startling and unappetizing.

There are also situations in which purple anthocyanin pigments turn an unappealing blue because of alkaline ingredients — events that are within the cook’s control. Blueberry muffins sometimes progress all the way into the green spectrum if large amounts of baking soda are used. If green muffins weird out your family at breakfast, baking powder, which is less reactive, can be used instead.

Reactive cookware such as iron or aluminum pots and pans can turn red cabbage an odd turquoise. I’ve learned to use stainless steel instead.

Here’s another theory: Some people might mistrust blue food because it’s the color of mold. Were the blue tortillas in the back of the fridge made with blue corn, or are they well on their way to becoming blue garbage?

On the other hand, some of the world’s greatest cheeses have been, by injection, imbued (imblued?) with a penicillin mold. The blue veins that result will not cure your pneumonia, but neither will they cause you harm. So if someone offers you a cracker spread with a fine Stilton, Roquefort or Gorgonzola, enjoy! It’s blue. Live with it.