You got a very nice pistol for the price!
The finish does not appear to be polished but blasted, if you sand the grip frame and then reblue it, it will look different. If you have access to a sandblasting cabinet you can prepare the steel properly and then rust blue the bare spot.
While rust blueing works great to repair smaller spots, the blueing might be of a slightly different color.
Deadite's suggestion to just leave it as it is, is not a bad one.