Q.Why Does My Lawn Have A Green With A Light Brown Color?
I have fertilized it; used Scotts disease EX

Certified GKH Gardening Expert
It appears to be the early signs of grass rust, but it could be a number of diseases. Depending on which one, your disease control of choice may not be effective.
Here are some articles that will help:
https://www.gardeningknowhow.com/lawn-care/lgen/brown-lawn-fixes.htm
https://www.gardeningknowhow.com/lawn-care/lgen/fixes-for-yellow-lawns.htm
https://www.gardeningknowhow.com/lawn-care/lgen/lawn-grass-rust-fungus.htm