On the first diagram, the y-axis is the absolute brightness of the stars in the visible spectrum (V) and the x-axis is the difference between magnitude in blue

On the first diagram, the y-axis is the absolute brightness of the stars in the visible spectrum (V) and the x-axis is the difference between magnitude in blue (B) and the entire magnitude of the star in visible spectrum (V). Thus on the left-top we will see super bright stars, all in blue spectrum, super hot blue stars actually. One is R136a1, a super massive blue star with 200 M and a radius of 4.7 millions sun! Although 163000 ly away, it’s still visible because of its super brightness. Those super-hot blue stars are just a momentary capture of quick giants, who is about to transit to other states entirely. On the right side, we will see bright red giants. A good candidate would be the Garnet Star.