【Gradation】 , 【shade】 ,  【nuance】  are comparable when they mean the difference or variation between two things that are nearly alike.

【Gradation】  in the singular implies a small difference or variation of this kind, but the term is used more frequently in the plural, so that it usually implies the successive steps by which a thing passes from one type or kind into something else of a different type or kind; thus, if we take the primary colors of the spectrum as blue, yellow, and red, the gradations between these are not the colors green, orange, purple, which are clearly seen, but all of the intermediate colors by which blue gradually passes into green, and green into yellow, and yellow into orange, and so on; therefore the word is often modified by some adjective (as sensible, apparent, perceptible, or imperceptible ).

【Shade】 implies a minute or barely perceptible degree of difference (as in thought, belief, meaning, or position).

【Shade】 is also often used adverbially in this sense with comparatives of adjectives or adverbs to imply a degree of difference that is barely noticeable.

【Nuance】 , though often interchangeable with  【shade】 , tends to stress even more the slightness or delicacy of the difference (as between musical tones, tints of color, or feelings).