A 6 billion year old white dwarf has the same temperature as the Sun.  We know that the color is the same because 
<ol type="a">
<li> The star started out with about the same mass as the Sun.
<li> Temperature is the most important determination of color for stars.
<li> All stars that die the same way have the same composition.
<li> At this age, it will be neither approaching nor receding.
</ol>