Watered = check
Used sharp blades to cut your turf = check
Set your mower deck to 3 inches = check
Not cutting off more than 1/3 of the blade when you mow = check
Fertilizing = check (more below)
And you still have an odd thing happening in your lawn where it seems to be dead grass but it has a tan or pink tint to it? Are they less than 1 foot in diameter? Hello Red Thread!
Red thread takes its name from the antler-like structures (sclerotia) produced by a fungus (Laetisaria fuciformis) on the tips of infected leaf blades.
Red Thread is a fungus that lawns get when they are over watered or there is too much rain (June 2013 in Connecticut!) and the nitrogen leeches out. The grass plants commonly affected by red thread include: Kentucky blue grass, perennial ryegrass and tall fescue.
What can you do to prevent it? Proper nitrogen in your soil is the beginning place to rid your turf of red thread. It may take up to 3 years of a full cycle nutrient program (5 applications for synthetic and 4 applications for organic) to rid your turf of red thread. In exceptionally rainy season (2013) you may need an extra application.
The good news is that red thread is a cosmetic fungus for the most part and it is only controlled by pesticides on sports turf and high value turf (think estates).