Bolts turned white and brown

These bolts are from my water pump. Are they re-usable? Also, anyone know what is the brown and white stuff? It looks like rust or corrosion, but I'm not too sure. Note: I also have a nice looking gold color one in the center that doesn't seem rusted. Maybe that one has better corrosion prevention or perhaps a previous mechanic replaced it?

http://i.imgur.com/OWgs7RY.jpg

Edit: Not sure how to delete attachments.^_^

I have found these bolts in this same state on every engine I have disassembled. I don't think it's a cause for worry. I just wire-brush them clean, and expect them to look the same in another twenty years or so.

Thanks! Just what I was looking to hear!