Linked from
The 9 pages that link to Spectral type, each with the reason it gives.
Blue supergiantRelated: Their blue color corresponds to hot spectral types, commonly O and B.
AldebaranRelated: Aldebaran’s K-type spectrum is consistent with its orange color.
AchernarRelated: Achernar’s blue-white appearance corresponds to a hot stellar spectral type.
SubdwarfRelated: The defining luminosity comparison is made at the same spectral type.