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I can certainly see the branding aspect. Why do you think they dropped the black macbook? Maybe because it looked like any other plain old wintel notebook when seen from any angle where you didnt see the Apple logo?
I do think that some nice colors wouldnt hurt. They do sell a significant portion of macs to people that dont need to look "professional". EG Students, Creative Pros, Audio Engineers, etc. I would likely go for Black anodized if they made it. (I'm one of those black wearing IT nerds!)
But a good Ferrari Red, Lamborghini Yellow or British Racing Green could be nice. Or even a good deep purple.
Though to go by what Sterling Ball of Musicman Guitars and Basses has to say on a similar topic. They offer dozens of colors for their instruments. Blue, green red, tobacco burst, vintage white, maroon, orange, grey, black, natural stained etc. But year after year, white and black outsell every other color.

It may be the same if Macs came in a dozen colors. They would sell a ton of black, a few reds and the yellow, orange, green purple etc would be in the "Refurb" store at the end of the year.
 
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