For those thinking of trying the MBs, but didn't take notes from the posts from a couple of weeks back, then see the section about colour coding in my post #5487.
You don't get the option to choose the colour when ordering from most suppliers, so you have to tell them. It seems to matter, as Golfnutz reckoned his Blues were smoother than the Greys.
I've only got the Blues (!), but had I understood the grading before ordering, I'd probably have gone for the Whites.
I tried to order some Whites locally and waited about 3 weeks. Then I emailed Customer support in the US, and was told the Whites do exist but are extremely rare. At that point I went back to the store and cancelled my order (had to pay a deposit and was refunded). I think the Blues are fairly common for any of the music stores that carry them.