Coral reefs are colored by eukaryotic chromoproteins (CPs) that are homologous to green fluorescent protein. CPs differ from fluorescent proteins (FPs) by intensely absorbing visible light to give strong colors in ambient light. This endows CPs with certain advantages over FPs， such as instrument-free detection uncomplicated by ultra-violet light damage or background fluorescence， efficient Förster resonance energy transfer (FRET) quenching， and photoacoustic imaging. Thus， CPs have found utility as genetic markers and in teaching， and are attractive for potential cell biosensor applications in the field. Most near-term applications of CPs require expression in a different domain of life: bacteria. However， it is unclear which of the eukaryotic CP genes might be suitable and how best to assay them.