They're saying that skin color is what people think is a reliable indicator of race, but in fact, genetically speaking, it's a total mess and nothing is clear at all.
Article even says it:
>The dark-skinned people of southern India, Australia and New Guinea, for example, did not independently evolve their color simply because evolution favored it.
>They inherited the ancestral dark variants Dr. Tishkoff’s team found in Africans. “They had to be introduced from an African population,” said Dr. Tishkoff.
They even admit there's some aspects to skin tone that are still completely a mystery, there's no genetic marker(s) they can point to as the cause.