In GT5 when you finish a race you are awarded prize money and experience. When the dialog appears to show you your experience increase there are 2 sections to the bar. The left hand portion is a solid colour; the right hand end is lighter, and fades in-and-out a bit. This happens for A-spec and B-spec XP bars as well as for the B-spec drivers' individual XP bars.
So, what do the 2 sections of the bar represent?