The Reason Why Piano Keys are Black and White

This is taken from a page on answers.com:
"Originally, white keys were made of ivory (white), and black keys of ebony (black). But any two contrasting colors will work. Many old keyboards present the "naturals" (lower tier) as black, and the sharps/flats (upper tier) as white!"

I think I knew the answer before, but I forgot. I easily forget things, so I needed to be reminded often. There is often this moment in life where you know you have learned it before, but your knowledge of it has just disappeared from your brain.