This White-eyed Vireo Vireo griseus was south of San Antonio, Texas, on January 01, 2015. What caught my eye was the facial pattern: the yellow supraloral band ends abruptly just past the leading edge of the eye, with a small, thin yellow arc next to the upper-rear quadrant of the eye. I looked at many photos of White-eyed Vireo on eBird and discovered that this pattern does occasionally occur. This pattern resembles that of Thick-billed Vireo V. crassirostris, and should be considered when assessing a potential vagrant Thick-billed Vireo.
More interesting to me was how much it resembles some Mangrove Vireos V. pallens. Mangrove occurs in two color morphs: yellow, and gray. The eye color of Mangrove Vireo ranges from dark brown through pale brown and dark gray to pale gray (in some almost whitish).
There is a discrete population of Mangrove Vireo on the upper Pacific coast of Mexico. This would seem to be the closest population to the U.S., but they only occur in the yellow form, and they are strictly associated with coastal mangroves. A vagrant from this population would not find syuitable habitat in the western U.S., and if one did occur it would stand out, especially as White-eyed Vireo is a vagrant to the western U.S.
The remaining population groups (Northern Caribbean; Northern Middle America (Pacific); Southern Middle America (Pacific)) occur in both yellow and gray morphs; the two other pacific coast populations tend to be mostly in coastal mangroves. By contrast the Caribbean population is widespread thoughout the Yucatan region, using a varety of habitats including disturbed scrub.
How likely is it that a Mangrove Vireo could get to the U.S.? Not very, but Yucatan Vireo Vireo magister has been found on the upper Texas coast, and comparing their ranges Mangrove seems more likely than Yucatan Vireo. Also note that there is a historic record of Black Catbird Melanoptila glabrirostris from south Texas - its range is similar to that of Mangrove Vireo.
What if a pale-eyed Mangrove Vireo that plumage-wise was somewhere between the drab gray morph and the strongly yellow morph were to get to Texas or Florida? It might be overlooked among the expected White-eyed Vireos. Conversely, any claim of such a vagrant Mangrove Vireo should be assessed with birds like this White-eyed Vireo in mind:
SEE BELOW the images for links to a number of Mangrove Vireo photos protraying individuals that resemble this White-eyed Vireo to varying degrees.
This is a link to the eBird photo page for Mangrove Vireo (300+ images).