There are two ways you could go about this. One wuld be to paint them, which would require taking them out and finding a suitable paint, I would guess they make a tinted clear coat you could find online or maybe at Vato Zone.
The second way would be to use a tinted film. We tint tail lights at work with a light smoked film, they are available from a variety of compaines. Install is pretty easy, cut the vinyl about twice the size of the light. Have two spray bottles, one with a 50/50 mixture of rubbing alk and water, the other with water and a little bit of baby shampoo. Spray both sides of the film with the water baby shampoo combo. Tack the film on the body of the runner above the tail light using the alk solution. Then stretch the film over the tail light and tack it down below the light. Use a tinters squeege to get the middle part of the film on the light. Then push the majority of the moisture out the sides of the light. Use a heat gun on the low setting and apply light heat while pushing the film around the rest of the tail light. Using the heat gun a squeege you will be able to shrink the film to fit the light. Use an Olfa or exacto knife (ALWAYS USE A FRESH BLADE) and trim slightly larger than the light. Use the heat gun again with a hard card and push the sides down. Everything should be heated and smoothed over. There will be some moisture still trapped under the film, dont worry it will dry out in a few days.
Or you could go and pay someone to do it. We charge about $60 to do two 4Runner tail lights.