"light as cotton on the something breeze, or is it air? I forget."

Probably Stephen Forster's 'I dream of Jeannie with the light brown hair / Borne as a vapour on the soft summer air.' Written in 1854, it didn't exist at the time Wide Sargasso Sea is set, but this is only one of many temporal inconsistencies in the text.

 

I Dream of Jeannie with the Light Brown Hair - a cover version by John McCormack