Motorists chose grey for 23% of new cars in 2019, according to the Society of Motor Manufacturers and Traders (SMMT).
This comes after the colour took the top spot for the first time in 2018.
This means three out of five cars joining UK roads were shades of monochrome.
The top five was completed by blue (17%) and red (10%).
The only new entrant in the top 10 was yellow, which replaced beige in 10th place.
Maroon, cream and pink were the most unpopular new car colours last year, taking a combined market share of less than 1%.
SMMT chief executive Mike Hawes said: "For most buyers, the colour is the first of many options they'll select on their new car, and today there are more possibilities to personalise your car than ever before.
"Drivers can choose from many hundreds of models equipped with the latest low and zero-emission powertrains, advanced safety and connected tech and exciting comfort and convenience features.
"There really is something to suit every driving need - and colour taste - on the market in 2020."
New car sales declined by 2.4% in 2019, with the industry blaming a number of issues including weak business and consumer confidence, political and economic instability, and confusion over clean air zones.