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With 7.53 billion people on the planet, it's estimated that 20 percent of the human population has some variation of brown hair. And, while that may seem like a low percentage, brown hair is the second most-common color in the world, right behind black. Some may deem light brown hair basic, but we see it as a universally flattering hair color with endless possibilities to play with undertones, highlights, lowlights, ombrés, and more.