Currently, it is generally accepted that chromophore synthesis of red fluorescent proteins proceeds via an intermediate “blue” form with a maximum absorption at 400 nm, which directly turns into “red” form due to the formation of a double bond in the side chain of the chromophore-forming Tyr residue. In the present work, we show that the synthesis of the chromophore of a chromoprotein from Actinia equina (aeCP) proceeds via dehydration and two stages of oxidation, like in other red fluorescent proteins. However, the appearance of an additional intermediate “green” form with a maximum absorption around 530 nm is observed.