You've probably washed all the nitrogen away with all that water. Fertilize it,
and cut the watering back to not much more than once a week.

Are you sure watering once a week would work in high-temperature Zone
9? We're hovering around 100 degrees most of the summer and I have to
hand-water dry spots frequently as it is. :/

What species is/are in the lawn? What have the temperatures been
like, day and night?

The lawn is a blue fescue mix. The daytime temps are in the upper
90's, low humidity, with nights in the lower 60s.

If by "blue fescue mix" you mean a mixture of Kentucky bluegrass and the
usual lawn fescues, you've probably got your answer right there. These are
cool season grasses and go dormant in heat -- you're probably seeing "leaf
firing". Continue to water, but do not overwater -- things will green
up again when fall comes.

If by "blue fescue mix" you mean you've got Festuca ovina var glauca,
it's also cool-season species, but one not suited for the typical
mowed lawn, as it's a clump-former, not a sod former.

Kay