Titanio(from pictures) seems to give the Enzo more depth per-se. It's a darker colour, compared with Argento. Argento is a little more flat looking. The deeper colours seem to give the Enzo a sort of mysterious look/feel.
I remember in the early prototype stages, they had the car with a seperate coloured roof. I thought I heard of that being an option, so you get sort of a 2 tone car...not quite sure abot yellow and corsa though.