Why its so hard to bring more colours to Xbox360 and PS3???

[Simulacrum]

Each new color of Ps3 have boosted hardware smoothly on Japan, but still we don't get new colours here...Just think how nice would white Ps3 slim look, I might buy it just for the looks (and since I got old model)

Few weeks ago Red Wii came to market,last year black Wii and it has boosted hardware nicely (holiday boost also etc), so why its so hard to bring, like 5 diffrent coloured Xbox360's and Ps3's to market?They would boost hardware like crazy on holidays.