1. Early Norse settlers: The most popular theory is that the name comes from the Old Norse word "blák," which means dark or black, and "ey," which means island. The Vikings, who settled in Scotland around the 8th and 9th centuries AD, may have used this name to describe the island's appearance. The island's dark, peaty soil and the thick forests that once covered it may have contributed to this name.
2. Scottish Gaelic: Another theory suggests that the name comes from the Scottish Gaelic words "blagh" or "blaich," which mean pale or fallow, and "innis," which means island. This name could refer to the pale or barren appearance of the island's landscape, particularly in the winter months.