The meanings of 'white’, 'black’ and 'red’ vary in English idioms and Chinese idioms, and so do their semantic extension patterns. This paper analyzes the semantic extensions of 'white’, 'black’ and 'red’ in English idioms and 'hóng’(红),'bái'(白)and “hēi (黑)in Chinese idioms in terms of Cognitive Linguistics, aiming at finding out their similarities and differences and their underlying cultural models. Conceptual metaphor, metonymy and metaphtonymy are discussed as the main means of semantic extension. English and Chinese idioms are collected from authoritative English idioms dictionaries and Chinese idiom dictionaries and instances of those currently used from 2011 to 2015 are collected from two corpora-- China Core Newspapers Full-text Database (CCND) and WebCorp. The findings indicate that different cultural models in the Mainland and English-speaking communities motivate the differences in semantic extensions of 'white’, black’ and 'red’ in English idioms and Chinese idioms. Keywords: color terms, semantic extension, metaphor, metonymy, cultural models