What discoloration?
Where do you live?
What seed did you plant?
How long ago did you plant?
What were your expectations (immediate germination? frost seeding?)

So cal, seeded 1 week today, tall fescue, there is a light brown discoloration that wasn't there before.

U can see it in the pic. It doesn't look like that anywhere else.

It's almost red

SoCal huh? My favorite pet peeve. SoCal includes everything west of a line from Bakersfield to Needles down to Yuma from below sea level to 10,000 feet. It can be 50 degrees and 115 degrees at the same time on the same day. Please be more specific.

If you are in the LA basin (south of the Tehachepi, Sierra Madre, San Gabriel and San Bernardino mountain ranges) and west of I-5 and the Santa Ana mountains to the south, you can get away with fescue all day long. East of that line it might get to be a battle with watering. If you are east of the Chino Hills or the Santa Anas into the Inland Empire, then fescue is guaranteed to be a watering issue. It can be grown in Indio so all is not lost. This is just to help you know what you might be getting into.

Gotta be honest: I don't see the color you are seeing. Colors are usually caused by different fungal diseases. Some are harmless. Fungal issues are usually a result of over watering. How long are you watering, how often, and do you know how long it takes your sprinklers to fill a cat food or tuna can? You should only be moistening the seed, not saturating the soil. We used to talk about watering new seed 3x per day for 10-1 minutes each time, but some of the newer watering systems can put out 1 full inch of water in 20 minutes. That is waay too much water for new seed. You need to figure that out for your system and water pressure. They are all different.

Those slightly lighter brown areas could be slightly drier as the other areas look pretty wet. They could also be soil salts starting to surface. The irrigation dissolves them or could be in the water, then the water evaporates from the surface leaving the salts behind. It could be you just have water high in lime, which the white stains on the walls suggest, and this is just the lime showing up as the water evaporates, or it could be other salts.

Just keep the soil moist without being wet, especially now that you have it well soaked.

Excellent points by beeone. I didn't think about salts or calcium. Really need to know where you live.