Diecasts and Sunlight

In the long term, direct sunlight and the heat can ruin the paint and othe parts forever. Painted plastic will most certainly whiten up. Best is to keep the cars displayed in a indirect light source. My hobby shop keeps the car under halogen lights at all times and there are blisters formed on the paint. The tires which are a rubber silicon compound deteriorate too.

All of AUTOart's boxes come with the warning : Long term exposure to direct sunlight or bright spotlight may cause damage.
All colored anodized items do tend to fade off when exposed to bright light. Transparent laquer may lengthen the time of the fading but the process is not foolproof. I guess its the same with waxes. I really dont think its a sure shot method to prevent fading. Like Lu says, UV rays is the real culprit here. There are UV resistant dyes and colors available but I really dont think they would be used on models of all things. Cost being a major factor.