Can you trademark colours?

Justice Stephen Breyer wrote: “Color alone, at least sometimes, can meet the basic legal requirements for use as a trademark. It can act as a symbol that distinguishes a firm’s goods and identifies their source, without serving any other significant function.”

It is incredibly challenging to trademark a color. The latest case of Cadbury losing its trademark over purple for its chocolate bar range to Nestle, who uses it for all of its good not just a single product, highlights this issue. But many have done this successfully, the most iconic example being luxury jeweler & retailer Tiffany & Co.
Their branding started in 1845 with the iconic ‘blue book’, whose shade changed till it settled on “tiffany blue”. In 1889, the hue was used in the display at the World’s Fair in Paris. Indicating the color association with the brand. Also, an orchid-shaped brooch from then (now owned by the Metropolitan Museum of Art) came in an elegant turquoise case —an early iteration of the now-iconic ‘blue box’ packing. By 1998 they trademarked its color and packaging and even partnered with Pantone to solidify its hue: “1837 Blue,” commemorating its founding year. No other trademarked color has become so closely associated with its brand.

References:

https://www.artsy.net/article/artsy-editorial-tiffany-monopolized-shade-blue

https://edition.cnn.com/style/article/tiffany–co-blue/index.html