Why is that we never use these terms interchangeably? I.e. one wouldn’t say “I’ve painted my walls a deep brunette”.
Why is it that “brunette” and “blonde” are used exclusively in reference to hair colour yet they just mean “brown” and “yellow”?
According to the OED both ‘blonde’ and ‘brunette’ are used exclusively in relation to hair colouring, occasionally extending to the complexions of the persons concerned.
The position is, I believe, much the same in French, from which both words emanate. Except that the City of Lille, Nord-Pas-de-Calais region, is home to the famous ‘blonde’ – a beer of distinction of the Pelforth brewery, now (perhaps sadly) owned by Heineken.