“Oh my gosh. It’s a bear. It’s a bear.” HGTV power duo Chip and Joanna Gaines debut a three-part limited series set in Colorado on Tuesday that packs plenty of surprises for the Waco, Texas-based couple — and a black bear sighting is just the beginning. The big picture: The new show, “Fixer Upper: Colorado Mountain House,” marks the first time the two have taken their renovation franchise beyond their home state. It takes place on a 1960s…