Chemists at the University of Washington in Seattle say their new colourful "smart" sunglasses could be the next big fashion statement.

Using polymer chemistry, they're developing sunglasses that will allow the wearer to instantly change the colour of their lenses to just about any hue of the rainbow.

"We've developed lenses that aren't like anything else on the market. This could be the fashion statement of the future," chemical engineer Chunye Xu said in a news release.

Xu says the lenses, described at this week's annual meeting of the American Chemical Society, will change colour by turning a tiny electronic knob in the frame.

So far, Xu's prototype can switch from transparent to blue, plus various shades in between. While the glasses currently look like a pair of laboratory goggles, they will eventually be manufactured to resemble the size and shape of normal sunglasses. Like regular sunglasses, they can be coated with a protective layer to block ultraviolet light.

"We are working on a multicoloured device as well, but no prototype is available yet," said Xu, who estimates the smart sunglasses will cost about the same as a normal pair.  She said she expects they will be available for sale in one to two years.

The lenses in the sunglasses use a unique type of electrochromic polymer that can change levels of darkness and colour in the presence of an electric current. The current comes from a tiny battery.