Why Are Carrots Orange (and Were They Always)?

Carrots are orange because they are packed with beta-carotene, a pigment that absorbs blue and violet light and reflects the orange and red that are left. They were not always orange. Wild carrots are white or pale, the first cultivated ones in Central Asia were purple and yellow, and the familiar orange carrot was selected by growers in Europe only a few hundred years ago. The molecule that makes them orange is the same family that makes flamingos pink, egg yolks yellow and autumn leaves gold. Carrots are simply the vegetable where it is most concentrated.

• Carrots are orange because of beta-carotene, which absorbs blue light and reflects orange and red.
• Wild carrots are white; the first cultivated carrots were purple and yellow.
• Orange carrots were selected by European growers a few hundred years ago.
• The same pigment family colours flamingos, egg yolks and autumn leaves.

Here is the chemistry, then the history.

Beta-carotene is a long, chain-like molecule with alternating double bonds, and it is those bonds that make it a pigment. Electrons along the chain can absorb light of particular energies, and for a chain of this length the energies fall in the blue-violet part of the spectrum, roughly 400 to 500 nanometres. White light falls on a carrot, the blue is absorbed, and the remaining wavelengths, yellow through red, are reflected back to your eye. Your brain adds them up as orange. Shorten the chain and the absorption shifts, which is why related molecules come out yellow; lengthen it or add oxygen atoms and you get the deeper reds and pinks.

No. The wild carrot, which still grows across Europe and Asia as a thin white root, is the ancestor. The earliest cultivated carrots, grown around Afghanistan more than a thousand years ago, were purple and yellow: purple from anthocyanins, the same pigments as blueberries, and yellow from milder carotenoids. Orange carrots appear in European paintings and records from around the seventeenth century, particularly in the Netherlands, where growers selected for sweeter, denser roots and happened to concentrate beta-carotene along the way. The story that they were bred orange to honour the Dutch royal house is popular and unproven; the more likely truth is that the orange ones tasted better and stored well, and the colour came along for the ride.

Yes, and they are increasingly easy to find. Purple, yellow, red and white varieties are all still grown, and a purple carrot cut in half often reveals an orange core, because the anthocyanin sits mainly in the outer layers while the carotene runs through. Red carrots, common in India, get their colour from lycopene, the same pigment as tomatoes. Every one of these is the same plant expressing a different balance of the same few pigment families.

Only if you were short of vitamin A to begin with. Beta-carotene is converted in the body to vitamin A, which is needed to make the light-sensitive pigment in your rod cells, so a genuine deficiency does cause poor night vision and carrots do correct it. But eating extra carrots on top of a normal diet does not give you better-than-normal night sight. The exaggerated version of the claim was encouraged during the Second World War as cover for Britain's radar, which is one of the better-documented pieces of wartime vegetable propaganda. The grey in the dark article explains what rods actually do.

Yes, mildly and harmlessly. Eat a great deal of carrot, or drink a lot of carrot juice, and beta-carotene builds up in the fat just under the skin, giving the palms, soles and face a yellow-orange tint. It is called carotenaemia, it is most common in babies on carrot-heavy purees, and it fades when the diet changes. It is the same mechanism, exactly, that makes a flamingo pink: an animal storing a dietary pigment in its tissue. The flamingo article follows that story to its end.

A great deal. Sweet potatoes, pumpkins, mangoes, apricots and the yolk of a free-range egg. Autumn leaves, where the carotenoids were present all summer and only show once the green chlorophyll breaks down. The feathers of canaries and the skin of salmon, via relatives of the molecule. And, in a modified form, the light-sensing pigment in your own eyes. One molecular family, one job, done everywhere.

Because of subtraction. A carrot does not add orange to white light. It removes blue, and what remains reads as orange. That is the same principle as every pigment, every printer ink and every colour filter. Hold the yellow face of a CMY Cube to a window and you remove blue; layer the magenta face behind it and you remove green too; the light that comes through sits between the two, and it is a clean, glowing orange. You have just made a carrot, without the chemistry.

Carrots are orange because beta-carotene absorbs blue light and reflects the rest. They were purple and yellow for most of their history and became orange through European selection a few hundred years ago. The same pigment family colours flamingos, egg yolks and autumn leaves, and it turns your palms faintly orange if you eat enough of it. Orange, like every colour, is what is left after something has been taken away.

Make orange by subtraction, and view colour through a different lens.