Looks like a lime hating Azalea.

Azaleas prefer acidic soil.

Upload, did you lime the garden recently? Mulching with shredded hardwood also drives the pH up. See the soil info here:
http://azaleas.org/index.pl/azculture.html

Some links about acidifying soil:
http://forums2.gardenweb.com/forums/load/tips/msg0308504123952.html
http://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/raise-acid-level-soil.htm

Has it been chronically overwatered?

I don't think the bed was ever treated with anything other than the mulch that was put down back in April.

Does anyone know if the light-colored leafs is generally a symptom of soil with high pH?

Also, these plants are right next to a sprinkler head that runs every day for about 15 minutes - I would say it's a lot of water, but enough to get the surface wet... since these are in direct sunlight for about 50% of the daytime, I'm really wondering if maybe they are getting under watered...

Quoting from the first link:

You may see localized nutrient deficiencies in particular plants. The most common problem by far is chlorosis, seen as a yellowing between the veins of the leaves while the veins remain green. It is caused by a lack of available iron due to a variety of reasons, including compacted soil, too much water, too much fertilizer, or soil acidity outside of the range needed by azaleas (pH between a low of 4.5 and a high of 6.0, where 7.0 is neutral)....

A calcium excess or deficiency appears the same as iron chlorosis to begin with, followed by leaf tip burn and twisted leaf tips.

Fifteen minutes every day isn't ideal for just about any plants. Better to change that to an hour every 3 or four days. Watering a little, often, dust dampens the soil surface and doesn't get to the roots of most plants - except for some shallow-rooted annuals. It creates week roots, and week plants.