Is protection against skin cancer a sufficient explanation for evolution of darker skin?

Partially: I would agree this is a component but the evolution of skin color is really much more multi factorial.

Possibly: But i also suspect that light skin is actually the evolutionary adaptation and that it occurred so that people didn't get rickets (severe vitamin d deficiency) as they migrated away from equatorial regions to higher latitudes where there is less uv driven vitamin d production. I also suspect its why scandinavian and alaskan native diets are rich in salmon and cod liver oil (tons of vit d).

Yes and no: The earliest humans evolved in Africa and had dark skin like modern Africans. Yes, the large amount of melanin is to protect furless skin against sun damage. But FAIR skin was the evolutionary adaptation to migration to more northern latitudes. We started out with dark skin.