That looks like St. Augustine to me. What I know can cause it to change colors like that are too much water (including rain) too much fertilizer (nitrogen) or not enough iron/PH is not right.
Put a small does of fertilizer a couple weeks ago. Been having alot of rain. My buddy mentioned having low iron and the same problem, so it could be that. I'll see if sunshine for the next weeks makes a difference. If not, I'll throw down some iron.
I'd guess it's centipede but you'd need to pull out a stolon.
The lines could possibly be where you added less fertilizer. The yellow areas also look like they may be higher than the darker green areas which could cause mowing height differences/more stress. I'd say an underfed lawn is more likely to show color variation though, just have to make sure not to overdo the nitrogen on a centipede lawn.
I get some of this in my lawn at green-up as well. I believe that it is just chlorosis, but I don't worry about it because in a few weeks the grass will be the same color throughout.
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