plainness

(noun) the state of being unmixed with other material. Example: "The plainness of vanilla ice cream."

(noun) clarity as a consequence of being perspicuous. Synonyms: perspicuity, perspicuousness.

(noun) the appearance of being plain and unpretentious.

(noun) an appearance that is not attractive or beautiful. Synonyms: homeliness. Example: "Fine clothes could not conceal the girl's homeliness."