Luminous novae named for having this property can be created when a star engulfs a planet or when two stars merge. Both the I (“eye”) band and a band quantifying this property are added to a common extension to the Johnson–Morgan system. The extent to which extinction from interstellar dust imparts this property is quantified by the excess of B-minus-V. Ionized H II (“H-two”) regions in other galaxies appear to have this property due to their strong H-alpha lines. Objects with this property have spectral type M, such as a class of dwarfs that are the most common type of main sequence star. This is the first property in the name of an evolutionary phase after the subgiant branch that ends with the helium flash. For 10 points, post-main-sequence (10[2])stars expand to become giants with what color? ■END■