It's been something that I've struggled with and Im not sure if I'm the only one whose wondered. Is the Vault Boy wearing a milti-colored jumpsuit, or is he wearing a yellow shirt with a blue button down? I suppose the obvious answer would be that it's a jumpsuit seeing as the pants are the same color, and all vault outfits in the games are jumpsuits, but I don't know that that is definitive.

Thoughts? Maybe I'm just crazy?

Maybe you are... The jumpsuit he wears could have been the orginal Vault design

The jumpsuit IS the original design- look at the player sprites for FO and FO2. Bethesda made slight modifications to the jumpsuit in FO3 (such as the "leather" cuffs, and that metal thing hanging off one of the shoulders.)

Shoulder plate?

Metal box with a tube going up and over the sholder. Left side, I think.