Colours represent the first human arrival in a given area.
Until around 12,000 years ago, much of the global north was covered by incredibly large and expansive glaciers. Before these glaciers receded, these areas were effectively uninhabitable. It follows then that the first inhabitants of these areas could only date back to at most 12,000 years ago. This period also saw the colonization of the islands of the Caribbean around 6000 years ago by archaic Caribbeans.