Unilever Canada – one of the giants of the food industry – was in a Montreal court Monday, saying it should have the right to make its margarine products the same colour as butter – something that's illegal in Quebec.

Unilever makes such well-known brands as Fleishmann's, Monarch, and Becel. But for decades, it's been unable in Quebec to add any colouring to its products that approximates the yellow colour that natural butter has.

So it's had to market two versions of its products in Canada – off-white versions in Quebec and ones that are butter-coloured in the other nine provinces. The dual production run costs it an extra $1 million a year.

Unilever lawyer Gerald Tremblay said Quebec's margarine law is discriminatory, prompted by pressure from the province's dairy industry.

"There is no doubt that colouration of margarine as enforced in Quebec constitutes an obstacle to trade," Tremblay told Quebec's Court of Appeal.

The Quebec government is fighting any change in the law, as is the Quebec Milk Producers Association. The milk industry says it has good reason to fight – saying consumers clearly prefer to buy yellow and are confused when margarine looks like butter.

Ontario has allowed yellow-coloured margarine for eight years. Other provinces either allow it, or don't enforce old laws that prohibit similar colouring.