I thought it was a Blue-gray Tanager but it seems to have a mask and some yellow near its tail.
Thraupis is a genus of birds of the tanager family occurring from Mexico to Argentina. Some are familiar species with large ranges. As currently defined the genus includes 9 species, but this includes species from two separate clades. Consequently, the genus is paraphyletic and two species (T. cyanocephala and T. bonariensis) are likely to eventually be moved to another genus.