The present invention provides nucleic acid compositions encoding a novel colorless GFP-like protein, acGFP, from Aequorea coerulscens and fluorescent and non-fluorescent mutants and derivatives thereof, as well as peptides and proteins encoded by these nucleic acid compositions. The subject protein and nucleic acid compositions of the present invention are colored and/or fluorescent and/or can be photoactivated, and can be used in a variety of different biological applications, particularly for labeling. Finally, kits for use in such biological applications are provided.