Is ARGENT Silver an original colour for an 81 VDP,cant see any reference for it.

Yes, argent silver is an original 1980-81 SD1 colour.

The series 1 was updated in 1980, several colours were added/deleted
then. The previous silver was 'platinum' which was quite different to
the argent silver (much richer/darker). Argent is similar to series
2 'silverleaf'.

The VDP replaced the V8-S, and what seems to be the case is that
all V8-S silver cars were platinum, all VDP silver cars were argent.

As with all series 1 colours, it's rare now!

many thanks