There are 2 different kind of front fender pieces being used through the 1970 model.
Type 1: a 1 piece model. The MACH1 letters are cast as 1 piece with the Rocker panel.
This type should be all Argent
Type 2: a Multiple piece model. The MACH1 letters are 'rivited' on the Rocker panel.
The Rocker panel part should be all Argent
The letters are chrome, with black.
These letters are sold by the aftermarket suppliers