Continuity mistake: During the Venice scenes, Ethan's hair length is always the same, except for scene number 1 where he and the team are on a boat arriving in Venice, and scene number 3 where he and Ilsa are on a balcony. In both these scenes, his hair is very short.
Revealing mistake: While inside the tunnel in Rome, before the yellow Fiat makes a U-turn multiple skid marks from previous takes are visible. Though one might pressume that the marks were already there, they are at the same spot and have the same pattern as the skid marks that the cars make seconds later.
Answer: While it looks like a normal Fiat 500, this is a specialised IMF car, as evidenced by the controls inside and its ludicrously high speed. It being electric is in line with that.