Starbucks on Monday revealed a new dress code for java-slinging baristas as CEO Brian Niccol bets on creating a comfortable, welcoming environment to boost the sagging company’s sales.

Starting May 12, employees will have to wear solid black tops, and will be issued two shirts from a new, company-branded line at no cost. Previously, the baristas were allowed to wear any color shirt they chose.

The workers must also wear khaki, black or blue denim bottoms. The prior dress code had allowed for gray and brown slacks or skirts.

“We’re evolving our dress code in all stores to focus on simplified color options that allow our iconic green apron to shine and create a sense of familiarity for our customers, no matter which store they visit across North America,” Starbucks said in a statement.

The coffee chain’s iconic green aprons – which have been around since 1987 – are such a staple that the company often refers to its employees as “green-apron partners.”

The stricter dress code is just the latest tweak under Niccol, who took the helm in September after orchestrating a turnaround at Chipotle as its chief executive.

He’s aiming to return the chain’s image from a grab-and-go shop to a sit-down cafe, with shorter wait times, trimmed-down menus and additional seating that could sway customers to linger longer.