Blue Stars are a type of Main Sequence star. They are the hottest type of star, and as such produce the most energy, even more than Yellow Stars.
This increased energy output enhances the Photonucleic Effect in Kryptonians and Daxamites; that is, Kryptonians and Daxamites living under a blue star would be incredibly powerful, even more so than they would under a Yellow Star. One of the abilities they gain from exposure to this type of star is Superman Vision.
Htrae orbits a blue star.