Blue budgerigars (Melopsittacus undulatus, second from the left) may be common in pet stores today, but when they first appeared in Europe in the second half of the 19th century, they were a rarity: In the wild, these small parrots usually have a green chest and a yellow head like the two birds on the right. Now, researchers have discovered that one tiny change in the birds’ DNA is enough to turn them blue. Most budgies are green thanks to a yellow pigment, psittacofulvin, mixing with a blue hue created by light bouncing off tiny structures on the birds’ feathers. Birds without the pigment end up with a blue chest and a white head. By sequencing the DNA from 234 pet budgies, 105 of them blue, researchers found that blue birds have a single mutation in a gene for a psittacofulvin-producing enzyme, they report today in Cell. The discovery will help map the evolution of parrots, the team says, the only birds that use psittacofulvins to color their feathers.