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The key ingredient (and how it works) The key to this lovely bit of colour-shifting magic is a special form of the dye version (not the lake version) of Red 27 (CI 45410) or Red 21 (45380)—though Red 27 is much more common. Under most conditions these dyes are bright, potent pink (Red 27 is a cooler pink; Red 21 is warmer), but below a pH of approximately 4, both are far less potent pastels.

Learn more: How do colour-changing lipsticks and blushes work? The science. from Lab Muffin

The key ingredient (and how it works) The key to this lovely bit of colour-shifting magic is a special form of the dye version (not the lake version) of Red 27 (CI 45410) or Red 21 (45380)—though Red 27 is much more common. Under most conditions these dyes are bright, potent pink (Red 27 is a cooler pink; Red 21 is warmer), but below a pH of approximately 4, both are far less potent pastels.