Earthy rustic tone means

Color! A lovely fern or lower light philodendron on the hearth and things you love on the mantel....a stack of books with a treasured ? on top (put this even on the hearth with perhaps a photo frame on top). Bottles collected at flea markets....a wonderful transparent bowl filled with coffee beans and a scented candle (use a softly colored large one on the hearth with perhaps 3 squat cream candles sitting in scented coffee beans, dry navy beans and some air plants), a wood animal washed with pale paint color....so many things. Choose a color range with a splash of pop from one item.

Add color needs pictures around to make it pop

Which color decorative stuff suits best for this fireplace ?

This photo of an "earthy rustic" room might help:

would depend on the colors in your room and whether it gets lots or little sun light. I'd start with basic colors in the light brown to cream range and add color. What style of furniture do you have - wood, upholstered, contemporary, etc.