The sun is just a hot mass like other stars. there is no fusion in the the stars.

The more mass attracted together by gravity, the stronger gravity it has, the higher energy density, the higher temperature it has. Bigger stars are hotter and oscillate at higher frequency bands.

There is no redshift, scientists today still don't know the true mechanism of light, they think light is something/photon/EM waves that propagating in vacuum space at light speed.