Your head will surely be white when you do it.
Just take a week-end off, shave and then hit the beach.
You'll be golden.
Kojack's right. I shaved my head on a Friday after work and my noggin was definitely white. I did hit the beach and by Monday when I went back to work, I was golden. It doesn't take long to get a tan on the dome. I've also tried self-tanning products, but nothing's better than the sun for getting a natural look.