Sounds like a nice welcome for you there!
I've been told the Blue hakama is a little more tradition because the dye was available earlier than black dye.
On the matters of Gi's we have several people who were black gi's within our organisation, and also a guy with Kendo/Iaido dan grades who wears his navy blue gi. (We even have a guy who wears a black Gi with a Yellow Hakama! Looks like a bumble bee!) It shoulds be noted though when we go to bigger national events everyone suddenly looks more orthadox in white with blue or black hakamas.
Ask your sensei - my guess is he'll say it's fine while your starting with them, but an investment in a white gi in the not to distant future would be advisable.