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 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.
Standing out
Ordinary is just ordinary, isn't it? With a white keyboard, your set-up looks just a bit more unique. You nicely break with the tradition of black and grey. With white, you can be nicely distinctive. This can still be subtle, by the way, because a white keyboard is just one element of your gaming set-up or workspace.