Whats the relationship between color and size of star?

Answer 1

The color and size of a star depends on whether it is included in the "main sequence" and how it has aged. Its size and color can change as it uses up its fuel. The larger the star the bigger its nuclear fusion furnace and the faster it burns its fuel and ages.

Answer 2

On the main sequence,where stars spend most of their lifetime, bigger stars are bluer and smaller stars redder. In other evolutionary phases of stars, they can be big and red (red giants) or small and blue (white dwarfs).