Yes you can – just put in a note and put in “custom color” for the case color option. No extra cost, but it may rust and I’m not sure about the surface quality – it won’t look like stainless steel! And it may become discolored or rust over time.
What are your plans?
No plans really, I just like the idea of a raw looking case. I would likely brush the aluminium and then put some sort of anti-corrosion clear over it, or figure something else out if the case ends up being zinc. Only the smaller case going out in the second run will come already anodized, correct?