Interesting note from Dan Moren, writing on Six Colors:

Something odd struck me recently as I perused the Apple Watch product pages. Several pictures of the Apple Watch Edition—aka the Super-Fancy Gold-That’s-Better-Than-Gold Spectacular model—show the center of the Digital Crown as different colors: I count black, white, navy blue, and red.

I think his theory that you’d choose a color for your digital crown when you purchase the device is correct. I doubt Apple would expect anyone to keep track of multiple tiny pieces like these. But, what’s the likelihood that Apple could swap them out for you if you took your Watch into an Apple Store?