Why are flamingos pink?

Flamingos are pink because of the food they eat, which is shrimp and algae.

Additional Input

It's not the the color of the food that makes the flamingo pink, but the chemicals inside.

Flamingos are pink if they have a lot of food containing beta carotene in their diet (i.e shrimp).

The coloring is actually a derivative of a class of plant-produced compounds called carotenoids-that is, carotene and its chemical cousins. Flamingoes in the wild eat shrimp, which is pink. The flamingo body may not process other colorful chemicals the way it processes carotene. Often times when flamingos are fed at a zoo, their diets are much different than their diet would be in the wild. Flamingoes in the wild eat shrimp, which is pink. Therefore flamingos in a zoo habitatand that aren't fed shrimp lose their pink color, so zookeepers must add food coloring to the food!

The depth and shade of their pink depends on how much suitable carotenoid they eat. In order to have flamingoes that remain pink in captivity, various colouring agents are fed to them; normally the same agents that are fed to farmed salmon so they have pink meat.

This answer is completely wrong! I'm pretty sure shrimps do not contain beta carotene. Beta carotene is an orange (not pink) pigment found in carrots and is a precursor to vitamin A. Whereas Astaxanthine is a pink pigment produced by plants and algae. It is Astaxanthine that give Flamingos their pink color. When shrimps eat algae the astaxanthine contained in them is incorporated into their chitin shell. When the Flamingos eat the shrimps the flamingos then incorporate the pigment into their feathers. Incidentally this is also why the meat or muscle of an adult wild salmon is pink. Farmed salmon raised on meal lacking the pigment have white appearing muscle. This is also why when you cook shrimp or lobster or crab they turn bright pink to red in color. Shrimps and lobsters don't look pink at first due to proteins in the shell obscuring the pigment. When the protein is denatured (cooked) it reveals the wonderful color. This is also true of the leaves of fall. When the green chlorophylls in the leaves are destroyed the reds and oranges and yellows of fall are revealed in their splendor! What about pink you say? I'll explain this next.

Both astaxanthine and beta carotene are Carotenoids, a group of pigment molecules produced by plants and algae that range in color from yellow to red (the leaves of fall). They help absorb light and pass the energy to chlorophyll. They can be divided into two groups, xanthophylls and carotenes. The former containing oxygen and the later lacking. The coloration of these molecules is due to the length of their carbon chain with alternating single and double bonds, called conjugation. This chain absorbs light of various colors (energies). The more highly conjugated or the longer the chain the more red the pigment looks. The shorter the chain the more yellow the pigment. Changing the length changes the light absorption spectrum and therefore the color. Vitamin A (retinol) alpha and beta carotene, lycopene, and lutien are all vitamins and antioxidants as well as Carotenoids.