If you don't think a system's color affects sales, then you need to read up on the "Little Purple Box", as detractors referred to the Gamecube in one of it's launch colors (the other being black). It was ridiculed from the start, and had to play catchup in terms of perception. Some people thought that it was geared only towards kids because of the color, even though it was more powerful than the PS2.
I concur that most core gamers would never not buy a system they want because of color, but there are MANY of us who would buy a new version of a system we already own for a cool color, like a jet black Wii. Then, of course, we sell our used Wii, and that pushes the used price of the Wii lower, which cause greater adoption of the system. You might be surprised by how many people will re-buy a system based on color. The DS has experienced that to the extreme in the past few years.
Hardware is only a means to enjoy great games!
