In our organisation, people wear black (or dark blue) hakama from shodan on. Before that, people may choose to wear white hakama from 5th kyu on. About 20% of the mudansha wear white hakama I guess, and so do I. It is a pain in the backside in a way, because it does get dirty quickly. IŽd never wear it outside my organisation though, as I was told that many organisations regard white hakama as only to be worn by O-Sensei. I wish we were more open in ref to hakama colours, IŽd love a burgundy one (and my husband, who is of Scottish heritage, would like to have a tartan one
).
I was told once that in Japan white has a similar meaning as black does in western society, but not sure if that is correct.