Can the sun change the color of the furniture?

Yes. UV rays and light can age wood and fabrics: a shade may lighten or yellow slightly depending on the type of wood (oak, acacia, pine, rubberwood) and the finish. Avoid prolonged direct sunlight, periodically rotate the objects placed (lamps, vases), and use a sheer curtain if the bay window is highly exposed.
Natural variations do not affect the quality.