The striking red soles of Christian Louboutin shoes are now the subject of a trademark case that could go to the Supreme Court. When competitor Yves St. Laurent released a line of monochrome shoes, some with a red sole, Louboutin filed a trademark claim and asked for a preliminary injunction on grounds of trademark infringement.

But a New York Southern District judge rejected the request, saying that a fashion house appropriating a single color is anticompetitive. Ballard Spahr IP Partner Hara Jacobs said that Louboutin’s next step will likely be to appeal to the Second Circuit as quickly as possible.

Said Ms. Jacobs: “It all centers on functionality. If the red sole is deemed functional rather than decorative, it can’t function as a trademark. So far, there is no cohesive test for whether an aesthetic feature is functional, so it is possible the Supreme Court will eventually take this case to rule on the issue.”