CI 42090 is a synthetic compound that gives a brilliant blue color to products such as shampoos, hair dyes and soaps. It is basically a dye that is widely used in the cosmetics industry. It is also known by other names such as Blue 1 CI 42090 or CI 42090 Blue 1. It comes in powder form and is very concentrated when used as a primary color. That said, it can also be mixed with other dyes to produce a wide range of hues and shades. The chemical formula for CI 42090 is C37H37N2O9S3. https://cosmetics.specialchem.com/inci-ingredients/ci-42090