When we view stars from the surface of our planet, they appear to twinkle. This is due to turbulence in the air, which creates air fluctuations that cause the starlight to deflect slightly. Since stars appear point-like due to their distance, the small deflections are enough to cause the star to twinkle.
Usually we just notice the variation in brightness, but air also acts like a prism, bending different colors of light by different amounts. So not only do stars appear to vary in brightness, they can also appear to vary in color.
Recently Roshaan Bukhari revealed this rainbow effect with the star Sirius. As he photographed the star, he shifted the telescope slightly to create a kind of time-lapse trail. You can see the result above.