Poa annua possibly?

Were there seedheads on it at some point?

Schaef said:

I thought trivialis was a really light lime green?

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It generally is a light green and has thick stems. Most of the patches in my lawn are circular in nature. Although poa trivilias gets seed heads it's typically mowed short enough that you won't see them. Whether annual blue grass (poa annua) or rough bluegrass (poa trivialis) they both tend to fade in the heat of summer.

If there isn't that much I'd start by hand pulling it.