I know JB Sod. Very well. They can grow sod but they are hopeless with maintenance practices. You are mowing way too short. Keep that mower raised up to at least 3" no shorter. The Pacific Northwest and cool grasses genetically have huge root systems. To support huge root systems the plant needs at least 3" with which to do photosynthesis to FEED those roots. If the grass is too short your grass is compromised, struggling. You will get weeds while your grass crop is weak. Don't use their fertilizer. Awful. I get in trouble every time I say this but try Dr. Earth's Lawn Fertilizer. Takes more, is far more slow but my goodness I forked out the money for this fertilizer to do commercial maintenance on lawns. I had my mowers custom raised for the correct height. I had multiple blades already sharped to perfection. The blades were cleaned with alcohol in between clients. Part of my service included aeration. Not an option. I always bagged clippings forget mulching!! Those stripes look suspicious...are you using a drop spreader? I used Scott's handheld cheapie spreader for everything other than ball parks. Much easier to control where that fertilizer goes. Never use weed and feed...forget moss control. Could you have your mower deck too short on one wheel? I know the Pacific Northwest and last I knew JB Sod was in the Kirkland/Woodinville area, yes? If you live there I can turn you on to the best BEST mulch for your beds; Sawdust Supply and Gro-Co. Lucky you!
This JB Sod is in Oregon or is the seed crop from Oregon? Same organization, similar environments. And watering practices are important; water very deeply and allow to dry out before watering again. Let us know what you've been doing exactly, what your automatic irrigation is set for, this doesn't look diseased. It looks like too short grass with a wheel too low on your mower or a very bad drop fert spreader. Let's figure this out before winter or you just very well have disease problems caused by stressed out wimpy grass. What exactly did you fertilize with? Sounds fine for your timing depending on the formulations you used. Don't need to aerate this year. Definitely next year. Train your grass roots watering very very deeply then do not water until you are able to see your footprints stay down when you walk on your grass. Then water again deeply...down at least 4"...this makes for very deep strong rootsystems where you won't ever have to worry about drought and watering this way reduces your water bill...if you are on city water.
One other possibility, how close do you live to a golf course? Poa annua our annual blue grass looks very straw colored, has lots of seed heads and thrives being cut short. Birds poop out these seeds and then your cool season grass mix of JB Sod's if stressed and cut too short will allow this light colored shallow rooted grass to become part of the lawn. Especially prominent living on golf courses. Golf courses up there love the ability to mow short short short and with a monocrop of this pale green color no one notices. The lawns of those that live on the golf course usually having used JB Sod on their lawns right next to huge expanses of Poa annua crops of the golf course are able to see this grass, looks like a dog peed on their lawn burning it to almost yellow. Most just had the lawn replaced over and over again. I ripped out lawns and replaced with plant beds, gravel, pavers and flagstone landscapes. They were very happy. Got lots of clients on golf courses for maintenance and landscape renovation projects.