I went to school with a pair of fraternal twins who were simply remarkable, and nobody ever believes me when I describe them. One of them was olive-skinned, with black, curly hair, and brown eyes, while his brother was milky fair with freckles, bright red, straight hair, and blue eyes. Other than that, though, they looked very much alike. Same height and build, and almost exactly the same features.
What odd sibs have you run across?