According to the article's aim to study English, Russian, and Hebrew idioms with the lexeme grey-gray / серый / (GRIS), a number of equivalents, original and unique GRIS were explored, the presented meanings of GRIS were organized into associative chains, then in microsystems, and the similarities and differences of trilingual GRIS were singled out. In the investigation, an extensive review of scientific literature in English and Russian was made and methods of qualitative-quantitative, semantic, and cultural-linguistic analysis in the framework of cognitive linguistics, color linguistics, and modern phraseology were used. The study consists of two main sections: Equivalent Grey Idioms (A. Optical color of natural objects and artificial objects; B. Mental and ethical problems) and Original, Unique GRIS. The quantitative and qualitative GRIS analysis convincingly proves an extensive basis for communication of multisystem linguistic and cultural groups, the intensity of interethnic communication in the 21st century, as well as the contribution of unique GRIS to the world linguistic culture. Optically grey color is between black and white, and, accordingly, GRIS are intermediate between black and white idioms, but are closer to black idioms. The article deals with the lexical-semantic polysemy of GRIS, and the metaphor "grey zone" that describes something intermediate, new, controversial, vague, not yet classified and regulated, and is intensively used in the 21 st century in technology, computer science, economics, trade, law, social work, medicine, morality, literature, and diplomacy. The work results will help in educational and translation practice, compiling dictionaries, and creating a base for automatic translation of phraseological units. The research also contributes to intercultural communication, psycholinguistics, cultural studies, cognitive and comparative linguistics.