I'm sorry, im still not understanding the use of "de" meaning "with" in 'les mains et les cheveux blancs de farine" what is the rule here?

Hi James,

So their hands and hair became white "from" the flour. De --> from (the origin of the whiteness, the flour)

That's how I see it.

Hope this helps.

Jim

Flour is an uncountable noun

Just to add to Jim's answer: in English you can also say: his hands were white of flour. This parallels the use of de in French.