This juvenile Black-billed Cuckoo Coccyzus erythropthalmus was at Rosehill Cemetery, Corpus Christi, Nueces county, Texas on the late date of October 27, 2013. I am struck by the fairly obvious and clean border between the off-white throat and apparently gray cheeks... rather more like a paler Blue-headed Vireo than a Cassin's Vireo! I feel that the multiple photos with light and shadows at different angles establish that this is not an artifact. My reference books do not mention or illustrate BBCU with obvious gray cheeks between the eye and the central throat, nor can I find any online photos of BBCU that show this - although a couple do have the faintest suggestion of such a feature. This unusual plumage effect is slightly more than esoteric, since one of the characteristic features of Dark-billed Cuckoo is that it has a contrasting gray band below the eye. Of course there are many other features that confirm the identity of this bird as BBCU.
For comparison here is a Yellow-billed Cuckoo from the same location and date, and in the same general lighting conditions; NOTE that the assessment is dimished by a fuzzy foreground branch across the lower throat; there is some contrast on the throat but no clean break line, and looks much more likely to be due to light/shadow effects: