Answer: I'd lift the sod up where it is yellowing to see if it is rooting (roots will be white). If it isn't rooting, scratch the soil to roughen it up and reset the sod, stepping down on it to help it make good contact with the soil. If you see new roots when you lift the yellowing sod, then the area isn't draining well and it may be developing a fungus. Adjust the soil level so the area drains better, then use a fungicide to control the fungus.
Best wishes with your new sod!
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