To be in line with Chameleon, it should be some bright colour to show "there's something special here". Chameleon ist bright yellow. ACA500 could be.. neon-green? Maybe orange would be a runner in *.nl? ;-)
With all the parts that need to be open (access to CF, A1200 accel connector), it'll be hard to make a full case. It might be just a steel cover, and a small part of the board will be visible. Last time I checked, it was cheaper to use stainless steel instead of cheaper steel with colour coating.
Should I decide to go with that design, the A1200 accel will always be openly visible. However, I'm not in a position to take suggestions or make promises at this point, where even the specs are not set in stone and software rights are not 100% clear.