Sentence:  You could say that inflexible thinking is <WSD>black-and-white</WSD> thinking and flexible thinking is rainbow thinking. <WSD>Black-and-white</WSD> thinkers have difficulty being flexible in their mind and seeing different possibilities and perspectives. 
Meaning of the word marked with <WSD> tags:  Classifying people, objects or concepts as two polar opposites, especially "right" and "wrong"; dichotomous and inflexible.