Not only the F-22 Raptor, but the Gripen, the F-35, the F-16 and many other modern fighters, to a lesser or greater degree, have a type of treatment on the canopy, to reduce the RCS (Radar Cross Section). The canopy (the transparent cover of the cockpit) is not made of glass, but of polycarbonate or plexiglass, which is a kind of acrylic. A sandwich of layers of these materials has between them a thin layer of some kind of malleable metal. Generally, an indium tin oxide alloy or even gold, as it is extremely malleable and, in the case of the F-22 and other fighters, is responsible for the canopy’s golden hue. The F-35 uses a less expensive aluminum-zinc composite, which gives the canopy a slightly pink tint.
The “pink” canopy of the F-35
What’s the point of this? It’s simple: the canopy is also “transparent” to the radar waves, which cross it and reflect on the backrest of the ejection seat, increasing the Radar Cross Section (RCS), which is the “radar signature” of the aircraft. And that’s not desirable in a fighter. Mainly in the F-22, which values for being stealth, or discreet to the radar. This thin layer does not make the canopy “penetrable” by radar waves, but it does keep it transparent to the pilot.
US Air Force F-16 fighter in flight. Note the golden tone of the canopy.
The interesting thing is that, on the F-16, this “golden” canopy replaced the original canopy, which did not have this treatment, being applied to the old aircraft, at the same time that the new ones left the factory with it. The crew didn’t like the new canopy, because in missions with NVG (Night Vision Goggles), it reflected the cockpit lights, getting in the way. So, it’s common to see some F-16s with the rear canopy section, which is fixed, gold, and the traditional front section, using the “old” traditional canopy.
USAF F-22 fighters in flight, with their golden canopies.