According to the Bible, all people — you, your neighbors, the guy who makes your coffee — came from Adam and Eve (Acts 17:26). The number of humans dwindled to the eight who were spared aboard the giant ship we call Noah's Ark — when God judged sinful humanity — and then we grew from there (Genesis 6–10). So, how did we end up with so many different skin shades? It's probably simpler than you think, but it will require some basic genetics. (Don't worry, we'll keep it simple.) Skin shade is governed by multiple genes and is quite complex, but for the sake of simplicity, assume for a moment that there are only two. Genes come in pairs of pairs. During reproduction, half of the genes passed on to the offspring come from each parent. For this discussion, let's assign the letters "A" and "B" to the genes that code for large amounts of melanin — the brown-colored pigment in everyone's skin. We'll also use the letters "a" and "b" to designate the genes for small amounts of melanin.
In very dark-skinned people groups, individuals carry AABB genes and only produce dark-skinned offspring. In very light-skinned people groups, individuals carry aabb genes and only produce light-skinned offspring.
If a male and female from each group mate and produce a child, the combination of their AABB and aabb genes would give rise to a child who carries the AaBb genes for melanin and would be "middle brown" in skin shade. Now, if two people carrying the AaBb genes got married and reproduced, their children could have a wide rage of skin colors.
If Adam and Eve were both middle brown (AaBb), they would have produced children with a wide range of tones. Suddenly, all of us being one race doesn't seem so complicated.