As you probably realize, astronomers must rely on the light that we can measure from the various astronomical objects. The spectrum of a star can tell us the temperature, size, and composition of the star. It can also tell us how fast it is moving. We can tell if the star has strong magnetic fields. Sometimes we can get the age of the star.
Stars come in colors from red, orange, yellow, white, and bluish-white.
The color depends on how hot the star is. Yes, sometimes it happens. For instance, two stars may start out as a pair in orbit around each other. Then some of the gas in the outer parts of the red giant may get pulled by the second star's gravity and get pulled onto the second star. A brown dwarf is a very small star, so small that it can't produce energy through nuclear reactions the way the normal stars do.