Calico Aster (Aster lateriflorus)
These are the tiny and slightly sloppy-looking aster flowers that peek out from hedges and pop up in cracks of sidewalks in September and October. The buds of the disk florets are bright yellow, but they turn deep brownish purple as they open. Both colors are usually present at the same time, giving the plant its calico pattern.
From Gray’s Manual: A. lateriflorus (L.) Britton. More or less pubescent, much branched ; leaves lanceolate or oblong-lanceolate, tapering or pointed at each end, sharply serrate in the middle; bracts of the involucre linear, acute or rather obtuse, imbricated in 3-4 rows. (A. diffusus Ait.) Thickets, fields, etc., very common from N. S. to Ont., and southw. Aug.-Oct. Extensively variable ; leaves larger than in either of the two preceding ; the involucre intermediate between them, as to the form of the bracts. Rays mostly short, white or pale bluish-purple.