I'd posit that the real cost is the cost of carrying more inventory. It's cheaper to carry 200 in beige than 100 in each of 10 colours. It means you're less likely to be out of the colour the customer wants and you don't have to track/manage the different options.
Compare with clip on covers for mobile phones. Heaps of colours/design available, but it's not a cost to the manufacturer as they leave all that up to third parties, who are effectively charging extra for the option of colour.
I'd posit that the real cost is the cost of carrying more inventory. It's cheaper to carry 200 in beige than 100 in each of 10 colours. It means you're less likely to be out of the colour the customer wants and you don't have to track/manage the different options.
Compare with clip on covers for mobile phones. Heaps of colours/design available, but it's not a cost to the manufacturer as they leave all that up to third parties, who are effectively charging extra for the option of colour.