Answer:
Stars that appear "red" are usually larger and cooler than yellow or blue ones. The color of a star is fairly representative of the temperature of an equivalent "black-body" radiation source, with blue being the hottest (O class) and red the coolest (M class stars).
Red dwarfs, because of the way they fuse hydrogen, are also red, but much smaller than any of the main sequence stars. The Sun will likely swell into a red giant, with a diameter up to 300 million kilometers, then lose mass and shrink to a white dwarf star.