From Olsen v. Lockheed:
"The F-22 requires numerous different coatings to be applied to the skin of the aircraft. The initial requirements were for three layers of coating to be stacked together in the following order: The first coating is a primer designed to smooth and seal the surface of the skin and promote adhesion of the conductive coating. The second is a conductive coating consisting of silver flakes mixed with polyurethane materials and intended to conduct, dissipate, and reflect the RADAR waves away."
There are a couple of reasons the airplane's base coating is silver, including:
- Using a conductive surface below the RAM layer makes both the RAM and shaping more effective
- The F-22 OML has many different materials - composites, aluminum, titanium, etc. - all with different electrical properties. The conductive coating effectively homogenizes the electrical properties visible to radar across most of the OML and keeps radar from seeing scattering sources inside the aircraft
From "Lockheed Martin's Affordable Stealh":
"Conductive Surfaces
A common misunderstanding is that composite skins are used to make aircraft stealthy. In reality, many composites are partially transparent to radar, and expose the internal structure, wiring and components to the radar, which is the last thing a low observable designer wants. These components add up to an extremely large signature. In most Low Observable aircraft, the outer surfaces of the aircraft are coated with a metallic paint, so that the radar cannot pen- etrate into the aircraft"
Most US stealth aircrat use a highly conductive "base" layer.
What you are seeing here is the F-22 with the conductive silver layer applied, but the other layers not yet applied. All F-22s have the same silver layer but you rarely see it as it is covered by the other layers - RAM, IR coating, etc.
