Reds and Yellows and any other pigments that use high percentages of those colours in their make-up tend to score poorly on the blue wool scale.
The blue wool scale is an industry adopted standard for the measurement of colour lightfastness. It was developed for testing textiles originally hence the name, but other industries involved in colour, paint, automotive and commercial printing all use this standard now.
They achieve this test by making 2 identical colour samples, they place one in the dark without any exposure to UV light and the other to direct sunlight or the UV equivalent, for roughly a 3 month period. The 2 samples are then compared against one another to see the amount of fading that has taken place. The results are rated between 0 and 8. With 0 being the worst and 8 the best, an 8 would be deemed to be perfect lightfastness.
In printing we use some special pigments that are mixed with other agents to give them lightfast properties. These are mainly the reds and yellows, oranges some purples too. But of all the colours we use, those pigments are more often than not the ones that will give the lowest blue wool scale.
It's the UV in sunlight that does the damage, there are polishes and sealants I believe that
help to block out UV's harmful effect. Suncream for the car anyone!
Seems that fading is the price you pay for some colours. Doesn't really offer a solution, the industry I am in is of course quite different to the automotive paints industry. But in colour typically many of the same rules apply.
