I've read a different hypothesis. For dark complected homosapiens coming out of Africa, waiting to gain a mutation for lighter skin, allowing for vitamin D to prevent rickets in their offspring, they would have first died off. So, it only makes sense that only through mating with enough Neanderthals to gain the gene for lighter completed offspring, and therefore not dying of rickets, would we (a Neanderthal/homosapien hybrid) have gained a toehold out of Africa.
People with dark skin can survive in Europe. As my previous linked article proves, quite a few dark skinned Europeans were walking around 10,000 years ago. However, in Europe's climactic conditions during the Stone Age, a European born with lighter skin will get more Vitamin D which will make him more vigorous and less sick, on average, than those born with darker skin. Hence the lighter skinned will have just a touch more offspring, which over the course of 100 generations or so adds up to the lightening of the whole group's skin color.
If the European Homo Sapiens needed dark skin to survive, so many Europeans would not be walking around 10,000 years ago when the Neanderthals went extinct 28,000 years ago. Unless Neanderthal is Bigfoot. In which case, he should get himself an agent, he can cash in big by coming out of the forest.