Probable Cassin's Vireo on Canon City,CO Riverwalk

I found this vireo on the Canon City Riverwalk yesterday and I believe it is a Cassin's, which is a rarity in this area. The top two pics show a lighter shade of gray on the head with an more indistinct margin between the auriculars and the neck area which is consistent with Cassin's Vireo. These pics are also consistent with a drab adult described in The Sibley Guide to Birds with greenish coloration to the secondaries (note: in order to preserve the coloration and shading, the only editing I have done on these pics is to crop them).

The bottom pic seems to show a darker head which would be more consistent with a Blue-headed Vireo but I think this is a result of the shading from the leaves though I did see this in several pics. SeEtta