Oil-based alkyd paints are extremely durable and you can scrub them frequently without affecting their color. Unfortunately, some of the chemicals in them can cause the paint to yellow over time. This yellowing is often subtle, but it's problematic with white paints -- which can experience a drastic color change as a result of this yellowing.
To stop your paint from changing colors, you can use a latex paint instead of an alkyd one. If you use alkyd paint, make sure it will get plenty of sunlight, and avoid using ammonia around the paint. Environmental factors can also play a role in keeping your white paint looking bright.
Shed Some Light
Light, both natural sunlight and artificial light, significantly slows the yellowing process of alkyd paint and can even reverse it. To prevent yellowing, use alkyd paint only in rooms that receive copious amounts of light. Frequently closed pocket doors, cupboard interiors and other surfaces that spend most of their time in the dark should not be painted with alkyd paint.
Choose Locations Carefully
Because of its superior water and mildew resistance, alkyd paint is often used in kitchens and bathrooms. If you use it there, make sure the white paint is not directly next to white tiles, countertops or cabinets. These materials are made to stay white, and include anti-yellowing chemicals and colorfast components. As a result, they will stay bright white, which will accentuate even a slight yellowing of the white paint on the wall.
Ammonia speeds the yellowing process of alkyd paints, so don't use it to clean in rooms where the paint has been applied.
If your renovation project includes more than a fresh coat of paint, make sure ammonia-based cleaners and stains are not used after the paint has been applied. Latex paints release ammonia as they dry, so apply latex paints before alkyd paints if you're using more than one type of paint. Let the latex paint dry for at least 24 hours, and be sure the ammonia has completely evaporated before applying alkyd paint.
Control Environmental Factors
Moisture, cigarette smoke and excessive cooking grease can all yellow any paint. Make sure leaks are fixed and resolve excessive moisture problems prior to painting. Install proper kitchen ventilation to curtail grease buildup, and don't smoke indoors. All of these measures can slow or even prevent yellowing of white paint in some instances.