Brass and SS were the same price, IIRC. I don't have the pricing for this one saved in my sheet, so I can't be sure.
Dark grey is a VERY hard color to do right, especially with this alloy of aluminum (6061), so I suspect that's why it's not quite perfectly grey. This is actually the reason the MIRA uses 6063, so that they can get the lunar grey to look right.
Every alloy of aluminum gives a slightly different color overtone, and every anodizing pool gives a slightly different color. That's why sometimes you'll see Chinese GBs talking about "bad pools." The benefit to 6061, however, is that it gives dark grey overtones to whatever color you anodize it.
Most of this information is available on the AAC's website,
http://www.anodizing.org/.
Fun fact, the AAC also regulates the price of the process, so it should never cost more than $150 (and even that is generous) to have something the size of a keyboard stripped and reanodized in the US. Generally the cost only gets raised if you need over 100 parts anodized, and that depends on the shop.
