I have been going to the zoo since 2003 and as far as I could remember they have always been painted blue (or white?). The zoo only has the pools in the aquatics section painted blue (or white), as well as some of the moats around the zoo. These exhibits will be destroyed soon to make way for the new Reptile House.
I noticed that the Dallas Zoo also has some pools in the River Habitat that appear to have been painted also.
Animaldude, I see you really like to know the names of each animal on display. Kind of adds a personal touch to them, making them more than just mere zoo residents I guess.