Grey? Blue? Purple? It can look different, depending on the context. Let’s talk about color perception, color temperature, and the history of laundry.
Atmospheric opacity image from ESA/Hubble (F. Granato): https://www.eso.org/public/images/atm_opacity/ – image licensed under CC by 4.0 – https://creativecommons.org/licenses/by/4.0/
The optical illusion is original, but based on the work of David Novick: https://twitter.com/novickprof/status/1139342022551191553
More on Illuminant D65: https://en.wikipedia.org/wiki/Illuminant_D65 – the references in this article go into the full technical detail
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