Life in the balmy tropics has made polar bears Inuka and Sheba go green with algae.

The usually white coats of Sheba and her 13-year-old son Inuka, Singapore Zoo's two polar bears, turned green a few weeks ago from algae growing in their hollow hair shafts, said Vincent Tan, a spokesman for the zoo.

"The harmless algae is the result of Singapore's warm and humid tropical conditions," he said.

Polar bears have clear hair shafts which appear white because they reflect light.