Cream is warmer and more obviously 'off-white' — it reads as a designer neutral. Buff is more oatmeal — slightly grayer, more 'pale beige.' Flax has the most golden warmth of the three and the most 'natural fiber' character — it reads as raw, fiber-forward, less designed. If you want a curtain that looks handwoven, Flax is the choice; if you want a clean designer pale neutral, Cream is closer.