A legal dispute between fashion labels Christian Louboutin and Yves Saint Laurent took a new turn yesterday when the jeweller, Tiffany, came in on the side of the shoe designer.

It filed an amicus curiae to support Louboutin's case that a colour can be trademarked and its use prohibited.

The case revolves around Louboutin's signature red soles and the accusation that YSL infringed copyright by selling shoes with soles in the same colour.

"We are enormously pleased that Tiffany has weighed in," Louboutin's lawyer, Harley Lewin, told fashion magazine Women's Wear Daily. "Tiffany has not only agreed with our arguments, but it also put forward arguments that strengthened the case."

Tiffany has a vested interest in the verdict, given that it filed a patent for its idiosyncratic duck egg-meets-turquoise shade of packaging in 1998.

Christian Louboutin first painted a prototype shoe's soles with scarlet nail varnish in 1993. Since then red soles have become a conspicuous status symbol, appearing on red carpets and pavements alike.