SeEtta et al,
Those look like the same aphids that have been attracting a lot of the late warblers along the Front Range. I think it is the Powdery Pine Needle Aphid (Eulachnus rileyi or related species in the same genus). Other warblers I have confirmed eating this same aphid of late are Blackburnian in Longmont, Yellow-rumped in Longmont, Yellow-rumped in Denver West Office Park, Palm Warbler in Denver West Office Park (per communication from Mark Chavez), Unknown warbler (probably Orange-crowned) in Denver West Office Park. In autumn's past, I have seen a Blackburnian in Greeley, a Bay-breasted and Northern Parula in Boulder and a Pine in Loveland going for this same aphid.
Nice photos and videos of a nice find by Brandon and Uncle Van in Pueblo City Park.
Dave Leatherman