Flexirubin is the main pigment in the bacteria genera Flexibacter, Flavobacterium, Chryseobacterium, and Cytophaga.

The pigment mixture of flexirubin and carotenoids imparts colonies with an intense yellow-orange color.

[2] Structurally, this bacteria pigment is based on a polycarboxylic-chromophore that is linked with a phenol by an ester, resulting in an alkyl side-chain.

[4] To test for the presence of flexirubin, a cultural strain with a 20% potassium hydroxide solution is created.

[1] Alternatively, the pigment can also be extracted with acetone and chromatographic methods can be used to ascertain its presence.