They'll change from red to green to blue very quickly, it' s almost like watching a Christmas light. All of the stars are close to the horizon and very bright. However, there are some close to the horizon bright stars which do not exhibit this behavior. The effect you're seeing is almost certainly due to refraction in the atmosphere. My son and I were trying to understand black holes and worm holes.
Stars have a LOT of mass.
Our Sun has more than 300,000 times the mass of the Earth, and it's only an average star. There are stars that are a lot heavier. They are so large because they are so hot, and the pressure from all the heat inflates them. The average density of a red giant is much less than one thousandth of the density of water. The pressure that has been holding up the outer layer drops, and the outer shells start falling toward the center.