La femme est debout. Deboute n'existe pas (débouté mais cela provient du verbe débouter) Tes cheveux sont de couleur... > De quelle couleur sont tes cheveux Tu peux dire aussi "Quelle couleur sont tes cheveux" mais c'est mal dit. De combien d'argent as-tu besoin? De quelle manière comptes-tu faire ce travail? Quant à grand-mère, c'est parce que c'est un mot composé et que grand est invariable

1. "de" = of. We don't ask "what colour..." we ask "of what colour..." It's just something we do. 2. no, "debout" is an adverb and they never change (even if feminine or plural). only adjectives and articles are coordinated with the noun. 3. grand-mère. I don't know. I think it got lost over time. Don't think of it as an adjective and a noun, think of it as signle noun made of 2 parts. (therefore the rules regarding coordination noun-adjectives don't apply).

Great. Thank you.

I learned today why grand-mère is spelled without "e". In old French, "grand" was invariable, so the feminine version was also "grand". It was only changed later to mimic other adjectives. There you have it!