AstraZeneca is seeing red over a purple pill.

For more than two decades, the drug maker has capitalized on a marketing campaign that labeled its two widely prescribed heartburn medicines – first, Prilosec and, later, Nexium –  as ‘The Purple Pill.’ The phrase and distinct look were used in a plethora of marketing materials, and largely succeeded in becoming synonymous with the medicines.

Recently, though, AstraZeneca began facing generic competition in the US for Nexium, the newer of its two drugs, and last month accused two different generic drug makers of ripping off its trademark purple look. In one case last month, AstraZeneca obtained a temporary restraining order that prevents Camber Pharmaceuticals from selling a version that is also purple, according to court documents.

Now, AstraZeneca has gone to court to prevent Dr. Reddy’s Laboratories, which is one of India’s largest generic drug makers, from selling another low-cost alternative. And in a lawsuit filed in federal court in Delaware, AstraZeneca accused the company of patent infringement and is seeking unspecified damages. A Dr. Reddy’s spokeswoman declined to comment.

The “purple generic pills are likely to cause confusion among consumers and others, and are likely to dilute the distinctiveness of AstraZeneca’s federally registered purple color trademarks,” the lawsuit states. AstraZeneca goes on to claim that Dr. Reddy’s is trying to get a “free ride off the fame of [the] famous Purple Pills, [which] poses imminent irreparable harm to both AstraZeneca and the public.”

In its lawsuit, AstraZeneca went out of its way to include several pages of photographs depicting promotional materials used in stores that displayed the ‘Purple Pill’ brand. And the drug maker also cited numerous media stories in which Nexium was referred to as the ‘Purple Pill.’

Whether AstraZeneca will prevail remains to be seen, of course. The drug maker has a point in that the marketing has created an impression that the ‘Purple Pill’ is a nickname for its medication. Ultimately, the tenets of trademark law will prevail. But a decision will likely be based, at least in part, on what a typical person may reasonably determine is similar – or not so similar –  between the pills.

“It’s unusual to claim trademark rights in colors. And the challenge is being able to enforce those rights,” said Matthew Cutler, an attorney at the Harness Dickey law firm who specializes in intellectual property. “You need to establish that your product is associated with that color. And you need to saturate the marketplace with that idea. It’s difficult because it takes many years and millions of dollars.”

He also noted that, if a company is not trying to trade on the goodwill of an established brand, why not simply make the pill a different color to eliminate any confusion in the marketplace?

However, some may argue that there is no confusion, since the pills do not appear to be entirely identical. A side-by-side photo that AstraZeneca filed in its court documents show the Dr. Reddy’s pill is purple, but not to the same degree as Prilosec and Nexium. As you can see in the photo, Prilosec is entirely purple, as is Nexium, which also has three small gold rings that run around a portion of the pill.

What do you think? Are two shades of gray enough to make a difference? Would you confuse the pills? Do you think others might be confused?