Besides the slightly yellow/green color, Is there something about the fine bladed grass that is not normal?

The fact that it is spreading eliminates just about everything except Kentucky bluegrass and creeping bentgrass. The fact that it is growing so well at the high mowing position practically eliminates bentgrass. Is this new grass creeping in from a neighbor's yard?

Does it grow particularly fast?
Does it send up seed heads before you can mow them?
Does it turn brown in the winter or summer?

When were the last two times you fertilized and what did you use?
When was the last time you overseeded?

Just out of curiosity, what is your watering regimen? How often and how long do you water?

Well, there's one or two other things I can think of rather than Kentucky bluegrass--Poa trivialis and Poa annua.

Fortunately, the color does not suggest either of those, and the shape of the blade looks wrong as well.

Would it be possible to get a closeup of the grass' ligule, plus a closeup of a blade and full grass plant? ID is easier if we have all the plant parts in front of us.

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Is there something about the fine bladed grass that is not normal? - I just find it very unattractive

Is this new grass creeping in from a neighbor's yard? - No

Does it grow particularly fast? - No

Does it send up seed heads before you can mow them? - I don't think so ???

Does it turn brown in the winter or summer? - Seems to turn brown later in the fall

When were the last two times you fertilized and what did you use? - Once this spring, regular fertilizer

When was the last time you overseeded? - I never have

Just out of curiosity, what is your watering regimen? - I water when I see the slightest sign of it drying out. I also seem to have poor soil conditions

While the ligule is membranous, the tip is not boat-shaped, it's more spiky. This does not seem to be P. annua or P. trivialis.

Consider yourself fortunate.

I have a feeling the result is going to come back, "barnyard grass," which means some random grass species (there are many). It seems to have a rhizome, so it's a spreading grass.

Let's see what others think--because I have no specific care regimen to remove it other than painting with Round Up individually or complete renovation.