Wii and Wii U are white because it leads to broader appeal, says Miyamoto

“Based on my background as an industrial designer and Nintendo and my background in creating entertainment, I’ve always wanted to make greater use of color in our hardware. If you look back on things like the Famicom and the original Super Nintendo, they were a lot more colorful from a hardware perspective. What we found over the years when we included a lot of different colors in our hardware is people would kind of point to that and use it to paint us as more kid-oriented. So really what we looked at is what are some ways from a design perspective that can make the system appeal to all ages. One of the ways that we found to best do that is to minimize the use of color. In that process we asked if we’re going to do that, what’s the best way to go? We found that rather than going all black - all white seems to have a broader appeal to people.” - Shigeru Miyamoto
 
Link