The reason for the bare-metal is that it was easy to maintain. The T-33 was an Air Force bird, and they didn't have to worry so much about corrosion; if you paint the thing, then you have to keep on re-painting it or else it starts to look pretty shabby. (And we can't be having with that at all.)

The Navy, seeing as how their whole job was to be near salt water, painted all of their aircraft.

The reason for the shiny bare metal finish is, well, shiny ones go faster.

True, but the level of polish on this one was quite remarkable. There's an F-86 two bays down that's still natural metal with none of this one's shine. Even Enola Gay, whose restoration was only completed about four years ago, doesn't gleam this mutch.

It's hard to tell from this picture, but the white paint underneath is quite crude, with a very fuzzy border. Like I said, there's bound to be a story behind this aircraft.