noun: the use of a particular key for writing a piece of music
noun: the range of colors used in a painting
noun: any of 24 major or minor diatonic scales that provide the tonal framework for a piece of music

Hughes
1871.—"There has been much written lately respecting colour and tone, but nothing bearing on your own view." "The new theories in music seem inclined to go back to the ancient faith of Pythagoras, everything being used up with the modern notions of tonality. Perhaps we may find a great change at hand; the present system, limiting, as it does, that which is illimitable, cannot be right." [Harmonies of Tones and Colours, Extracts from Dr. Gauntlett's Letters1, page 48]