Why is the sun round and yellow?

Take an odd shaped piece of something flexible and spin it. The laws
of gravity will make it 'even all round' so that one part is not
sticking out and causing an imbalance. Its the spin of stars and
planets that make them round. The yellow colour is part of the light
spectrum involving heat. Just like flames in  fire. For you
astronomers out there, please dont be too harsh.

Hi pugwash,

   Your heart's in the right place, but you're not right about spin
causing roundness. The Sun's spin isn't the principle cause of its
sphericity. That is generally due to the fact that gravity pulls all
the Sun's mass equally inward, toward its center. Spin actually tends
to distort the Sun away from a sphere and flatten it somewhat. Were
the Sun rotating rapidly enough, it'd actually fling mass right off
the equator.

   On the other hand, you're essentially right that the Sun's color is
due to its temperature, pretty much as a candle flame. Various stars,
with a variety of surface temperatures, display a variety of
predominant colors.

In relation to colour, the Sun is yellow as it is in the spectral star
class 'G'. This means its temperature is between 5000-6000 Kelvin and
the strongest spectrum lines are from calcium ions and atoms, and
other metal atoms. The strongest of these lines are of yellow light,
hence the Sun principally emits yellow light.