The Twinkle Factory labeling technology is a novel tool that enables the specific fluorescent labeling of any protein of interest. This technology is based on the instantaneous formation of a fluorescent molecular assembly between the small (14 kDa) protein tag FAST and various fluorogenic ligands. Twinkle Factory's Fluorogens strongly fluoresce only when bound to FAST, enabling to detect and image FAST-tagged proteins with high contrast without the need of washing the excess of fluorogenic ligands. The labeling of FAST-tagged proteins with a Twinkle Factory's Fluorogen is non-covalent and can be reversed if necessary by washing. By using different Twinkle Factory's Fluorogens, the spectral properties of the FAST-tagged protein can be changed without the need to switch protein tags, providing an experimental versatility not encountered with fluorescent proteins.