Flamingos are pink when they ingest the beta-carotene in their natural food. They can become less pink after breeding or in zoos. The old-fashioned way of keeping them pink is to feed them with foods rich in beta-carotenes. These days, zoos might include an artificial additive to their food. One thing's for sure: the pH of the lake has nothing to do with the pink colouration. It's true that flamingos can tolerate water with a higher pH value than many other creatures can, but the alkaline condition of their habitat is caused by things like dissolved carbonates, not by dissolved salt. Which is what brine is.