Christian Louboutin (plaintiff) was a French designer of women’s footwear and accessories. Louboutin’s shoe lines always featured lacquered, bright-red outsoles that contrasted sharply with the colors of the uppers and soles. After 15 years of increasing commercial success and recognition, Louboutin trademarked his characteristic red-lacquered outsoles as the Red Sole Mark. Yves Saint Laurent America Holding, Inc. (YSL) (defendant) began selling a series of monochrome shoes. Each shoe’s upper, sole, outsole, and heel were one color. YSL created its monochrome shoes in purple, green, yellow, and red. Louboutin sued YSL for trademark infringement, seeking a preliminary injunction to prevent YSL from selling any shoes with outsoles that used the same color red as the Red Sole Mark. YSL filed counterclaims against Louboutin, alleging that the Red Sole Mark was invalid because the mark was either: (1) ornamental rather than distinctive, or (2) functional. The district court denied Louboutin’s request for a preliminary injunction, finding that Louboutin was unlikely to succeed on the merits of his claims. The district court reasoned that trademark protection could not be extended to a single color in the context of the fashion industry. Louboutin appealed.