Not sure if there is a "standard" color. If you mean the lenses, most mfgs use either a smoke or clear. Smoke colors vary with mfger and year run and age.
Go to a local PPG type glass company and ask them to show you their Lexan color sample(s).
If you're replacing originals with new portlights from Lewmar, Gray, Pompanette, etc. to match the frame color, you'll get the color choices they have at the time you order. Some brands yellow with age, some don't.