Michael Chetrit has worked on many construction projects with interior designers during his 15-year tenure at The Chetrit Organization, a real-estate investment firm founded by his family. The 36 year-old Parisian native once believed that "all interior designers do is shop, and it’s so easy, there’s nothing to it." When he combined two apartments he owns in a Midtown building, he resolved to do the decorating himself.

"Then I googled ‘light fixtures’ and got over 600,000 choices. I gave up right away," he said.

The wetbar has custom cabinetry and bar stools designed by Ms. Bikoff.

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Lesson learned, Mr. Chetrit turned to his friend, the interior designer Sasha Bikoff, for help combining and furnishing the two apartments, for which he paid $988,942 and $1.55 million respectively. It was an unlikely pairing. Ms. Bikoff, who says she would "never want to practice restraint in interiors," has become known for her skillful use of bold colors and patterns (her staircase, a multistory mélange of crazy colors and patterns, was the much-Instagrammed runaway hit of the Kip’s Bay show house in New York City two years ago.) Yet, Mr. Chetrit, she says, "had no interior design style, didn’t know what he liked or didn’t like, and described himself as ‘a simple guy.’" Mr. Chetrit admitted, "I wanted something not too crazy, but I had to give her some leeway. I am a finance guy, not a creative guy."

It took 18 months, and $650,000 on renovations and interior design, to create the 2,700-square-foot, three-bedroom space that Ms. Bikoff describes as a "gentlemanly bachelor pad, in comfortable neutral tones, with hints of color." Mr. Chetrit moved in during January 2019.

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The color palette wove in subtle nods to Mr. Chetrit’s Moroccan heritage (his parents were born in Casablanca). While it is a departure from her usual style, Ms. Bikoff educated her client on the aesthetic benefits of incorporating vintage pieces in the design plan and layering textures.

The color palette of a guest bedroom was inspired by menswear.

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The result is her goal of creating one or more "moments of excitement" in each room: the Midcentury-inspired chest in one of the guest bedrooms or the 1970s tessellated horn nightstands in another. Her biggest stylistic scores were the powder room, clad in black and white terrazzo tiles and the adjacent foyer, with walls covered in an abstract palm print.

Mr. Chetrit had the most input in the kitchen—a priority for him as a passionate cook and frequent host. His penchant for a clean, minimal space was realized at Scavolini, an Italian maker of minimalist, architectural case goods and other home furnishings, which customized the deep indigo color of the cabinetry. Mr. Chetrit had worried the color might be too specific, screaming "bachelor pad" and not family friendly. Today, he says, "every single person who walks in comments on how beautiful it looks."

The powder room walls are clad in black and white terrazzo tile.

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Here, he has all he needs to cook well, including a five-burner cooktop (the fifth burner is larger, to accommodate a wok), two ovens, a teppanyaki grill and two refrigerators. Ms. Bikoff chose to cover the island in mirrored gunmetal glass to add warmth and reflect the wood floors, which are set in a chevron pattern. She created continuity between the kitchen and dining areas with a table made of marble that closely matches that on the backsplash and countertops, set with custom chairs in a fabric with a geometric pattern that, Ms. Bikoff felt, nodded to Moroccan motifs, as did the modern, lantern-like shapes of the pendant lamps hung above.

The adjacent living area was a compromise. "As a designer I am style over function, but my client was function over style, so we had to find a happy medium," said Ms. Bikoff of the space. In the end, the client got the requested maximum lounging capacity with three sofas, and she sourced a wood and mixed-metal credenza, space-age stools, and vintage coffee table that she tied together with a vibrant blue rug.

A backgammon table centers the "game room" area; Mr. Chetrit is an avid player. "Any real backgammon player will tell you that part of the enjoyment of the game is having a really nice board. It’s like playing tennis with a nice racquet versus a bad racquet. I really wanted a nice board." His wish was granted, courtesy of Hector Saxe, a Parisian company that custom made the table in colors to complement the space.

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This custom backgammon table was custom made by Parisian company Hector Saxe.

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Ms. Bikoff gives ample credit to her client, who, she says, trusted her and made decisions quickly.

In return, Mr. Chetrit credits their long friendship, open communication, Ms. Bikoff’s willingness to adapt and her "great taste." When asked what he’d learned from the process, he conceded, "If you want to do things well, you have to hire a professional."