All stars are born with the same basic composition, yet stars can differ greatly in appearance. which two basic factors are most important in determining the current appearance of a star?

The two basic factors which are most important in determining the current appearance of a star are its mass and its stage of life. Stars are born with 75% Hydrogen and 25% Helium, with no more than 3% of that being heavier elements. A star burns its supply of elements over its lifetime, the larger the mass of the star then the greater it's brightness, luminosity and surface temperature will be. Dependant on the stage of the star's life, the color of the light will change.