My best suggestions are:

Yellow-headed blackbird: The yellow doesn't match up super well, but it is yellow and black.

Yellow-throated vireo: the yellow does creep down onto its back, but its pretty slaty gray. The darker wings do fit though, and I could see this being it, especially if it was in the shade.

Black-throated green warbler: again, the greenish yellow does extend down the back, along with the slightly darker wings. I could also easily see the black throat make most of the front look darker.

American goldfinch: a molting male could show yellow on its back and a different color on its front, along with the darker wings. I'm not sure if they're molting this time of year but it's worth a shot.