And those paints that stay white in sunshine and yellow in the shade do so because of the catalysts in the paint that bleach the binder in sunlight. Sadly it's been so long since I did proper chemistry that I can't recall which catalysts do this. First formulated by ICI I think and used in Dulux paint.
For extreme environments there's a tendency to apply a two-pack urethane top coat varnish that screens UV from the layers below which stops colours from fading but may encourage white finishes to yellow.
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