Can you even out skin color over a sun poisoning scar?

Possibly camouflage. Scars can be noticeable for a variety of reasons, including texture and color, location and appearance. Depending on the reason for why it is noticeable, it can be camouflaged or improved, with techniques such as makeup, microdermabrasion, laser (or other light based therapy), surgery, or tattooing.
Yes. Most of the time, if you allow the skin to heal and not damage it with further sun exposure i.e.Use sunblocks and cover up, the color will even out. If there is hyperpigmentation (dark pigment), we might lighten it with bleaching creams or skin lighteners. Peels may also even the color and in the worse case scenarios with permanent blotches we may use combo rx /camo tattoos.
Possibly. Hyperpigmentation can be difficult to entirely correct, but the most common treatment is a bleaching cream, usually with hydroquinone. This should only be prescribed by a dermatologist or plastic surgeon knowledgable in treatment of such a condition.