[vanderZwan]

The argument in favor of it is that Monet was an exceptional trained painter, and one specialized in colors on top of that. He might have been extra sensitive to colors compared to most humans (both in the sense of biological sensory sensitivity, as well as trained ability to perceive colors).

[animal531]

It is possible, if somewhat unlikely, for men to also be tetrachromats.

[vanderZwan]

Color vision is encoded on the X-chromosome, right? And human tetrachromatocy depends on having two X-chromosomes with different color vision genes[0]. So wouldn't a hypothetical tetrachromatic male need to be an XX-chromosome male[1], and on top of that have one of the X-chromosomes carrying the deutanomaly, protanomaly or tritanomaly mutation, and on top of that have this mixture manifest itself as having four color receptors instead of three? Or is there another theoretical way that I'm missing?

If my educated guess is correct then "somewhat unlikely" seems like quite an understatement to me! :D

(I have protanomaly myself, and never considered that men could hypothetically be tetrachormats as well. This was a fun through exercise)

[0] https://en.wikipedia.org/wiki/Tetrachromacy#Humans

[1] https://en.wikipedia.org/wiki/XX_male_syndrome