Short answer
Their colour comes from carotenoids — long, fat-soluble molecules whose chain of alternating double bonds absorbs blue and violet light, so they look yellow, orange or red. Carotenoids tolerate ordinary cooking far better than chlorophyll or anthocyanins; what fades them is long exposure to oxygen, light and high heat, which break or rearrange the chain. Their colour also depends on what they are bound to, which is why a lobster turns from blue-black to red when cooked.
A carotenoid is built from repeating five-carbon units into a long chain with many alternating single and double bonds. That conjugated system lets electrons absorb light in the blue-violet part of the spectrum; what is left to reach the eye is yellow, orange or red. The more double bonds in the conjugated run, the further the absorption moves towards longer wavelengths and the redder the pigment looks. That is the difference between yellow lutein, orange β-carotene and red lycopene: not different kinds of chemistry, but chains of different effective length.
Carotenoids sit in fatty cell structures and do not dissolve in water, so boiling does not leach them out the way it leaches water-soluble pigments. They are not bound to a metal that acid can knock out, and ordinary cooking temperatures do not break the chain quickly. Cooking often makes them look stronger: heat softens cell walls and releases the pigment into the surrounding fat, which is why the oil around roasted peppers or a tomato sauce turns orange. The losses come from oxygen and light over time — dried apricots and paprika fade in a bright shop window — and from very long, very hot cooking that can bend the chain into less intensely coloured forms.
Animals cannot make carotenoids; they eat them. Salmon, trout, prawns and flamingos get their pink and orange from astaxanthin and related pigments in their diet. In a live lobster the astaxanthin is bound inside a protein complex called crustacyanin, which shifts its absorption so strongly that the shell looks dark blue-black. Cooking unfolds the protein and releases the carotenoid, whose own orange-red colour appears. The pigment was there the whole time; the cooking changed its surroundings, not the molecule.
Farmed salmon gets astaxanthin in its feed for the same reason wild salmon has it from krill and shrimp: without it, the flesh would be pale.
Carotenoids sit alongside chlorophyll in every green leaf. They are masked because chlorophyll absorbs so strongly across the red and blue. When chlorophyll breaks down — in a ripening pepper, a yellowing banana skin or an autumn leaf — the carotenoids already present become visible, and some fruits add more as they ripen. A green pepper and a red pepper are the same fruit at different stages, and the red one's colour is mainly newly made capsanthin and capsorubin.
Why: Light and oxygen oxidise the carotenoid chain.
Fix: Store in opaque, airtight containers away from light.
Why: Carotenoids are fat-soluble and migrate into oil as cell walls soften.
Fix: That is expected; the colour is in the sauce, not lost.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
Carotenoids are fat-soluble isoprenoid pigments whose colour arises from a conjugated polyene chain; they are degraded mainly by oxygen, light and heat.
Source: Chemistry, Occurrence, Properties, Applications, and Encapsulation of Carotenoids—A Review
FactModerate evidence
A live lobster's dark blue colour comes from astaxanthin bound in the crustacyanin protein complex; cooking releases the carotenoid and reveals its orange-red colour.
FactStrong evidence
During ripening, fruits typically lose chlorophyll and accumulate carotenoids and, in some species, anthocyanins, which drives the change from green to yellow, orange or red.
Source: Fruit ripening: dynamics and integrated analysis of carotenoids and anthocyanins; Molecular and Hormonal Mechanisms Regulating Fleshy Fruit Ripening
FactStrong evidence
Carotenes and several other carotenoids (paprika extract, lycopene, lutein) are authorised EU food colours with their own E numbers in the E160–E161 range.
Source: Food colours (topic page)
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.