Red stars are the coolest. They are usually between 3,000-6,000 degrees Fahrenheit. They include Proxima Centauri (4.2 light-years from Earth) and Betelgeuse (350-650 light-years from Earth). The...
Color from a "black box" (i.e., a ball of gas with no intrinsic color) is a function of it's temperature. Much like heating a piece of steel in a fire - first it glows red, then yellow, then white,...