I would think the colour surcharge thing has to do with the (relatively, compared to say an iPod) small numbers they're creating. I don't know much about factory costs, but I would have to think that if you're pressing a gazillion of them, it's easy enough to absorb the different costs for different casings. With the number of eDGes in production, perhaps not so much.

That was my thought when I saw the extra charge, anyway. Sure I would rather have not paid for it, but at the time of pre-order for a first-gen product, I just figured that Entourage had decided it was worth offering different colours even if small runs were expensive enough they'd have to charge the customer more.