If you live in Japan this option has already opened up to you. As a Nintendo member you can not only pick colors, but also how many colors your Switch will arrive with. Sadly, this won't be the case for those who like North America as well as other locations. There will only be 2 color options.
1. Neon Blue and Red
2. All Gray
Let's clarify something real quick, those outside of Japan will still be able to have different colors, but they will have to do so one piece at a time. The different colors for the many different pieces of the system will be sold separately.