The oldest stars are now mostly either white dwarfs or neutron stars. A few of the largest may be black holes.
yellow
Speaking in astronomical terms there is no determined color for old dying stars. It just matters what type of star it is. For example, red giants like Betelgeuse or Antares are the most common stars...
the color of the star indicates how hot the star is
No. It is just a knowing of a temperature. Red is cold, and blue is hot. Our sun is yellow which is the middle.