Mariah Carey. Picture: AP

The 'All I Want For Christmas Is You' hitmaker enjoys wearing one of a kind pieces for her live shows and music videos, and stylish Nicolas Bru explained how she "usually" has a good idea about what she wants.

He told PEOPLE magazine: "She doesn't like to try on a hundred things. I usually try to get clothing made for her because she likes custom dresses, especially for her concerts and music videos.

Mariah Carey performs in Las Vegas. (Photo by John Salangsang/Invision/AP)

"She's been doing this for a pretty long time so she's very aware of her body and what looks good on her. She usually has a pretty good hunch as to what's going to work.

"She's also pretty eccentric -- if I feel like she should try something, she'll try it on and give it a chance. She'll tell me, 'I'm not sure it's going to work but I'll give it a try'. Sometimes it does, sometimes it doesn't."

Bru - who also collaborates with stars like Fergie and Sofia Carson - described his work with Mariah as a "really easy" because of her willingness to try "new ideas" despite having a vision in her head.

He explained: "She's never really asked for specific things. She gives me a vibe and I know what she likes and what looks good on her. I don't think she's ever gone, 'Oh, get me this.'

"I think she knows what she likes and she expects a certain quality of work but she is really fun and really easy to collaborate with. She's open to new ideas. It's a nice working relationships for sure."