Fluorescent proteins from the GFP family have become indispensable imaging tools in life sciences research. In recent years, a wide variety of these proteins were discovered in non-bioluminescent anthozoa. Some of them feature exciting new properties, including the possibility to change their fluorescence quantum yield and/or color by irradiating with light of specific wavelengths. These photoactivatable fluorescent proteins enable many interesting applications including pulse-chase experiments and super-resolution imaging. In this review, we discuss the development of advanced variants, using a structure-function based, molecular biophysics approach, of the photoactivatable fluorescent protein EosFP, which can be photoconverted from green to red fluorescence by -400 nm light. A variety of applications are presented that demonstrate the versatility of these marker proteins in live-cell imaging.