Painting gives a great color depth for plastic or metal parts. If a maker or hobbyist can properly clean their parts after machining, prepare the surface finish, apply a primer if needed, and then apply one or more coats of paint plus a clear coat they can totally achieve amazing results with great color depth. Many makers and hobbyists use spray paint and with good part preparation they get great results. https://www.wikihow.com/Spray-Paint-Plastic . In situations where paint is to be used, having a base color similar to the paint means that small chips, cracks or other damage to the paint through normal wear and tear will be less obvious. In situations where people do not want to go through the careful steps for a great paint finish, or where they are concerned about the odors and health effects of the paints, molded in colors can be a good option. Painting requires a well-ventilated area and the personal protective equipment such as a proper filter mask, goggles, gloves etc which people may not have. In applications such as kids toys, the durability of the molding in colors is an advantage.