How does a star's appearance change based on the elements inside it?

Other than hydrogen and helium which are always in approximately in the same proportions, the rest make up only trace elements totaling up to 2% of a star at the time of its formation. But they do affect the appearance and even evolution of the star. Most importantly they make the star less transparent to light, so that more heat is retained in the interior. This causes a greater tendency toward a red giant stage and the pulsing effect in Cepheid variables. Carbon stars in particular have their appearance altered by heavy elements, however. If more carbon exists in the star's atmosphere than oxygen (transferred from the interior through convection), the excess carbon will give the star a red color like soot in earth's atmosphere will make the sun appear red.

The stars composistion gives the compustion its material so different materials burn differently ex. brighter darker whiter bluer blacker redder

Ireally don’t know

It maybe because uranus is made of gas but uranus has a solid core in the middle