We're completely convinced Spock knows what colour he is. He's taken to sleeping in or on black things all of the time. When you nearly step on him, pick up the bag he's in or just walk by and it suddenly moves it can be a little disconcerting!
He was even carrying around Sadie's Purina bandana from the Walk for Dog Guides for awhile. I think for Spock it's a bonus when things smell like Sadie.