Is this your Color class or an existing one? For an existing one, why not just pull up the source and find out?
Otherwise, you need to learn about how ints are represented in binary, and how colors are typically packed into ints. There are many many such encodings, but a typical one is RGBA, where the most significant byte in the int is the red component, followed by Green, Blue, then Alpha at the least significant byte.http://www.khanacademy.org/science/computer-science/v/binary-numbers
When you've watched that, go here next:http://en.wikipedia.org/wiki/Bitwise_operation