Sage sets the whole mood here, and it is a lovely color to work in. This soft, grayed green is quiet enough that it never competes for your attention, which is exactly what you want when you are trying to concentrate. It has a gentle, leafy calm that makes a home office feel like a restful place rather than a stressful one, and it flatters both bright daylight and a warm desk lamp at night.
To keep the room from feeling flat, lift the edges with Cream on the trim, baseboards, and window frames. It is warmer and softer than a stark white, so it frames the sage without any harsh contrast and keeps everything feeling cozy. Then add a few touches of Walnut through your desk, a bookshelf, or a frame to give the space some weight and richness. Sage on the walls, cream around the openings, walnut in the wood you bring in, and you have a calm, grounded office that is easy to sit in all day.