I think the boot colour is a bit of a red herring , the c5's are obviously all very similar.
There are several differences that aren't so obvious - the main one being the spec of the motor.
Adam Harper told me that there are three variants , some being slightly quicker on the flat than standard, whilst some others were better going up hills, but were also slower on the flat.
We're not talking massive differences here, just a few mph , and it was down to the windings in the motor. There is no way of telling them apart unless you dismantle the motor and count the windings.
Other differences are the width of the final drive cog coming out the gearbox where some are much wider than others.
Starting to sound a bit like an anorak now so I'll end it there