Chief justice of Karnataka P D Dinakaran's car violates the law by sporting number plates in red and gold, a transport official said.
It should have black letters against a white background, according to central motor vehicle rules.
Legal experts said there are no provisions for judges to use number plates in red and gold.
"That's obviously a mistake," said Justice M F Saldanha, former judge of the Karnataka high court. "Neither a chief justice or judges of the high court can use colour schemes other than the ones mentioned in the motor vehicle rules."
Transport officials are equally certain the colours are not permissible.
"When it comes to number plates, the law is the same for everyone, from the man on the street to the prime minister. The only exceptions are the President of India, governors and foreign diplomats," said a senior official in the transport ministry.
The number plate also sports the three-lion emblem of India, seen on vehicles used by the President of India and state governors.
The President and the governors travel in official cars that bear the emblem in gold, embossed on red plates. Their vehicles have no number plates.
Rule 50(2) of the Central Motor Vehicle Act gives clear guidelines on colour schemes.
The law lays down the use of black letters against a white background for private cars, and black letters against a yellow background for tourist vehicles.
Vehicles belonging to foreign consulates are prescribed white letters against a blue background, and vehicles belonging to the army have a unique numbering system, unlike private and tourist vehicles.
High court registrar R B Budhihal said, "The government allots cars to judges. You can obtain further information after filing an application."
Law minister S Suresh Kumar said, "I haven't seen the number plates. I would prefer not to comment until I am sure about the details."
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