When Nintendo released the Wii U in November 2012, they only showed off the system in both black and white variations. The white version is for the basic set while the black version is for the deluxe set. If Nintendo were to announced future colors for Wii U consoles, would this bring in more sales? It's possible that sales for the system would increase, but they would have to be very careful with the color choices.
If Nintendo, out of completely nowhere, released a purple Wii U console, it could very well be in high demand due to it's color alone. If Nintendo also decided to release the colored console with a 500GB or even a 1TB HDD, you can bet that more and more gamers will get the system due to them not having to buy an external HDD if they don't already own one. What if not everyone likes purple and wants a Wii U with an increase HDD? All Nintendo has to do is release a few limited edition colors and keep them on the market for 6 or more months. Purple, Silver & Red would be excellent choices for a limited deluxe edition of the console, but if they are poor with color choice, they could end up with a 3DS-related problem.
In North America, Nintendo's 3DS Handheld is only available in red, blue and pink. Gamers everywhere are patiently waiting for a black or white edition of the system and we're still stuck with old colors. Most Wii U owners want a black or white 3DS so their systems will be matching, but if Nintendo releases a pink, red or blue Wii U before the black or white 3DS systems, gamers could have matching systems as well but nobody wants a generic color.
In the end, Nintendo should have a black and white version of all their systems with other colors in the future. They're switching up this formula for the 3DS but it could all lead to future sales in the long run. Nintendo has not confirmed the existence of a colored Wii U system but it's always possible. After seeing all of the 3DS colors that are being released in other parts of the world, it'd be odd for Nintendo to keep the same black and white console scheme.