When the U.S. Court of Appeals for the 2nd Circuit hears oral arguments later this month in shoe designer Christian Louboutin’s appeal to protect his trademark on red lacquered soles, the court will be presented with two starkly different views of what purpose color serves in fashion design.

Louboutin, who is known around the world for the flashy Chinese red on the bottom of his posh high heels, will argue that the colored soles serve only to identify the Louboutin brand. Louboutin’s red soles, according to the designer’s lawyers at McCarter & English, are purely brand ID, just like Owens-Corning’s pink fiberglass or Tiffany’s robin’s-egg blue packaging. (Tiffany filed an amicus brief endorsing Louboutin’s interpretation of color and trademarks.)

Yves Saint Laurent has countered that Louboutin, by his own admission, had an aesthetic purpose for lacquering the soles of his shoes red. So, according to YSL’s counsel at Debevoise & Plimpton, Louboutin is not entitled to a trademark under the U.S. Supreme Court’s 1995 opinion in Qualitex v. JacobsonProducts, which holds that a color can be trademarked only when it “can act as a symbol that distinguishes a firm’s goods and identifies their source, without serving any other significant function.” When color serves an aesthetic function (as YSL contends it does in Louboutin’s shoes), it cannot be trademarked.

On Wednesday, YSL’s interpretation of trademark law got a boost from a group of 11 law school professors, who filed an amicus brief in support of YSL. “This court should recognize that the shadow cast by a mark in a single color on a fashion item creates enormous uncertainty for other designers and should regard claims of single-color trademarks in fashion with considerable skepticism,” the professors asserted in a brief written by Rebecca Tushnet of Georgetown University Law Center.

Interestingly, the law professors’ filing argued that if the 2nd Circuit permitted trademarks on colors that serve an aesthetic function, it would be muddling the distinction between trademark and patent law. Trademarks aren’t supposed to confer the same sort of monopoly power as design patents, and Louboutin’s broad assertion of its trademark right on the color red was anticompetitive, the brief said. The professors, like YSL’s lawyers, distinguished between Louboutin’s red soles and Tiffany’s blue boxes, which don’t impinge design choices of other jewelers.