Monochromatic stainless steel is the same as regular stainless steel. The word 'monochromatic' means 'having one color or hue.' Designers use the term to indicate that the entire outside of an appliance is stainless steel or gray--that is, that the appearance is uniform.
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Monochromatic stainless steel is a term used by the appliance industry for their stainless steel appliances who's body and dispenser areas are gray to blend in with the stainless of the front.