Nestle has won a court battle with confectionery rival Cadbury, over Cadbury's attempt to trademark the purple colour of its Dairy Milk bars.
Last year Cadbury won a legal case to stop other chocolate firms using the colour - known as Pantone 2865c.
But Swiss firm Nestle, the world's biggest food company, has now won an appeal against that earlier ruling.
"Cadbury's formulation does not comply with the requirements for [trademark] registration," said the UK court.
The Court of Appeal also said the trademark application lacked "the required clarity, precision, self-containment, durability and objectivity to qualify for registration".
The legal battle has been running since 2008, when Nestle first opposed Cadbury's initial trademark application.
Cadbury - bought by US food giant Kraft in 2010 - has been using a purple colour on its chocolate wrappers since the early 20th century.
"We are disappointed by this latest decision but it's important to point out that it does not affect our long held right to protect our distinctive colour purple from others seeking to pass off their products as Cadbury chocolate," said a Cadbury spokesman.
"Our colour purple has been linked with Cadbury for a century and the British public has grown up understanding its link with our chocolate.
"We are studying this particular ruling and will consider our next steps which includes the possibility of an appeal."
Nestle said it welcomed the court decision, which it believed "was the right outcome from a legal perspective".