Start with Soft Yellow on the walls. It is a gentle, buttery tone rather than a bright lemon, so it fills a nursery with warmth and light without ever feeling loud. That soft glow is lovely first thing in the morning and stays calm enough for a darkened room at bedtime, which is exactly what you want where a baby sleeps and plays.
From there, Cool Gray on the trim and door frames gives the yellow a clean, quiet edge and keeps the whole room feeling fresh. For a little contrast, bring in Charcoal Gray on the things that move around the room, like a dresser, a bookshelf, or a single accent wall behind the crib. So it is simple: yellow on the walls, the softer gray on your trim, and the deep charcoal saved for one piece or wall that grounds everything.