Does anyone know how to give palm/coconut leaves that cream color?

yes when we are in AZ for winter

Do you want to darken it? Or do you wish to lighten other pieces like it? Wood stains can darken it and I've had luck bleaching palm and other woody materials in the bathtub with laundry bleach and water and then laying them in the sun for a few days.

Try 2 tablespoons milk with several cups water. Just apply with soft cloth, let dry .

I had a neighbor across the street from us that used furniture polish to make her house plants look fantastic, if that is what you were asking. She also used it in the shower walls and bathroom walls to keep them from attracting minerals and soap scum.

Jokeing

Palm or coconut fronds as they are called achieve that pale white wash color by laying them out in the sun to dry

Yes. That would be a DRIED leaf..