I recently came across an interesting trademark dispute that involves the rights to red soles on women’s shoes. Like many trademark law topics, this issue is not that simple.

The shoe designer Christian Louboutin is known for his distinctive red glossy soles. He registered what is called a “color mark,” presumably giving him protection from others who try to sell similar shoes. When the worldwide fashion house Yves Saint Laurent began selling shoes that were entirely red with red soles, Louboutin claimed a violation of his trademark rights. This gave rise to the current lawsuit between the two companies, which is pending in a federal appellate court.

The right to protect a color, or more accurately, design as a trademark, is rather complex. If a color is deemed functional, such as green for farm equipment, it cannot be trademarked.

There’s little doubt that the marketplace identifies and differentiates this color with John Deere equipment. John Deere can take advantage of this recognition, but it cannot prevent other farm equipment manufacturers from using green.

The same seems to be true with Caterpillar’s yellow road machines. Caterpillar does have trademark protection for its “Caterpillar Yellow” logo. However, yellow is a functional color for road construction, so Cat can’t prevent other companies from manufacturing yellow-colored equipment.

On the other hand, if a color has no functional value but merely identifies the maker, it can be protected. Consider Owens Corning fiberglass insulation, which since 1956 has been dyed pink. The company was granted a trademark on the color “PINK” (in capital letters only), and uses the Pink Panther cartoon character as a visual representation of its brand identity.

But let’s get back to fashion. Here it can go either way. It can be argued that Louboutin’s red soles are not functional…that is, their only purpose is to identify the maker of the shoes. Or it can be argued that in fashion, all colors are functional, and it would be unfair to prevent a designer from using any particular color.

This is the issue that a federal appeals court will rule on soon. What’s certain that in the end, one of the parties will see red.

Jeff Lapatine is the group director, naming and brand architecture, for the Siegel+Gale New York office.