My two issues/questions:
1) I just noticed today that the places where the blades are much thinner/srawnier and darker, I cannot poke a 1/8" metal stick down past 3". Stick bends. Lushy places, stick does down 6"+. Will it help if I aerate my new sod by poking holes in the ground all the way till I reach 6"+ inches of easy poking? I understand you cannot aerate new sod for at least a year. I tried using the sandals just now and was horrified that they were actually pulling up the sod from the soil.
2) What's wrong here -- when I cut it (leaving it 2-3" tall), each blade has a yellow inside and top, but green lush sides. Weird. You'd think it would be fresh green all around. I look closely and the cross section is green on outside, but yellow inside. What can cause that? Is this bad? My husband says to quit fretting about it because it's the best lawn in the neighborhood, but it seems wrong to me. I did have a grub problem 3 weeks ago, but used insecticide and I'm guessing they're gone. Grass is consistently like this, it's not a new thing. Always with the yellow insides, green outsides.

Thanks in advance!

Please name the town you live in in SoCal. I grew up in Riverside, went to school in Pomona, worked in Downey and Hawthorne, and had relatives in Los Angeles (the real Los Angeles), Stanton, Palm Desert, and Indio. Sometimes I can help with details that most people would not be aware of.

I would wait a few weeks for the soil to dry out before making judgements about the soil. One thing you might do is to apply a thin layer of compost. Let's see, if you have 400 square feet then 1/2 yard of compost is all you need.

Normally I would say that mowing the grass that short might result in seeing the yellowish blades, but that grass is a dwarf variety and should not show yellow.

How do you know you had a grub problem and which insecticide did you use?