After all the dents are hammered out, the car is coated with an acid etching primer. The etching primer, which appears as a greenish-gold in these photos, bonds to the metal and gives the subsequent layers something to stick to.
The etching primer is followed by an epoxy primer, not shown in this series of photos. The epoxy primer binds to the etching primer and seals the car to prevent rust.
The epoxy primer is followed by a high builds primer. The high builds primer, which is gray, dries to a hard finish that is then sanded away by a process called blocking.
As the car is blocked, any slight ripples or imperfections in the metal are filled leaving a perfectly smooth and flat surface to paint over. It is the smoothness of this surface that allows a High Performance Finish, which this car will receive, to really pop.