The Hatter has 2016 white and 2017 black socks in his drawer. He takes two socks out of the drawer without looking. If the socks he takes out are of the same colour, he throws them away, and puts an additional black sock into the drawer. If the socks he takes out are of different colours, then he throws out the black sock, and puts the white one back. The Hatter continues with his sorting until there is only one sock left in the drawer. What colour is that sock?