Readability
First of all, the advantage of readability. It is much more pleasant for the eyes to read black letters on a white background than white letters on a black background. If you can't touch-type, then a white keyboard is also a user-friendly advantage.
Hygiene
A common counter-argument for a white keyboard is that it's quite prone to showing dirt. Every speck of dirt that lands on it immediately reveals itself. We say: great! Because who wants to work on a dirty keyboard? If your keyboard starts to show some spots, you'll know it's time to clean it. This can be done very simply with some compressed air (or a puff of breath) and a lightly damp cloth.
Aesthetics
White is modern, sleek, stylish, professional, minimalist and clean. In certain workspaces where white is dominant, smaller items such as a mouse, keyboard and mouse pad can complete the overall look. Whether you're an intensive gamer, a designer or doing administrative tasks, everyone can add the finishing touch to their workspace with a white keyboard.
Stand out
Ordinary is just ordinary, isn't it? With a white keyboard, your set-up looks just that bit more unique. You nicely break with the tradition of black and grey. With white, you can be wonderfully distinctive. This can still be subtle, by the way, as a white keyboard is just one element of your gaming set-up or workspace.