Fire is a chemical reaction, it gives off matter (ash, soot, and smoke), heat, and massless photons as byproducts. The photons given off by fire are called incandescence. What you see is based on the photons and the frequency they vibrate. Fire will typically be red and orange which are lower on the spectrum. Stars can be a bit different and often give off photons higher on the spectrum. They can display colors like blue or white which are emitted photons with waves properties vibrating at a higher frequency (and more energy) than your typical fire.