Three subspecies of Plain-colored Tanager recognized (Storer 1970):
rava Wetmore 1963; type locality Almirante, Bocas del Toro, Panamá
Occurs in southeastern Costa Rica and western Panama (western Bocas del Toro)
Similar to languens, but differs by "having the throat, lower breast, abdomen, and undertail coverts distinctly pinkish buff; blue of lesser wing coverts definitely darker" (Wetmore et al. 1984).
languens Bangs and Barbour 1922; type locality Loma de Leon, Panama
Occurs in Panama and in northwestern Colombia (Chocó; extreme western Antioquia)
Similar to nominate inornata, but upperparts paler, and with a less pronounced bluish tinge on the forecrown and rump; throat and flanks also paler gray (Hellmayr 1936, Wetmore el al. 1984).
inornata (Gould 1855); type locality Santa Fé de Bogota [Colombia]
Occurs in northern Colombia (upper Sinú, lower Cauca, and middle Magdalena valleys). Populations in the upper Sinú valley are intermediate between nominate inornata and languens.
Plain-colored Tanager is a member of the genus Tangara, which includes more species than any other genus of Neotropical birds (Isler and Isler 1987). Tangara contains 49 species, which Isler and Isler (1987) divided into 13 species groups based on their distribution, appearance, behavior, vocalizations, and nest sites. Tangara inornata and Tangara mexicana (Turquoise Tanager) were placed in Species Group 1. Both species are found in semi-open areas within forested regions, but inornata occurs to the west and mexicana occurs the east of the Andes (Isler and Isler 1987). They both utter rapid, high-pitched notes. Plain-colored and Turquoise Tanagers differ from other species of Tangara in that they live in very small groups of 4-6 individuals and they rarely are joined by other species (Isler and Isler 1987). The close relationship of these two species has been confirmed by phylogenetic analyses of molecular sequence data (Burns and Naoki 2004, Sedano and Burns). This species group is monophyletic. Together, these two species are most closely related to a clade containing the species Tangara chilensis (Paradise Tanager), T. callophrys (Opal-crowned Tanager), and T. velia (Opal-rumped Tanager) (Burns and Naoki 2004, Sedano and Burns 2010).