Makes me wonder if there was some innovation in the production of violet pigments around that time. I recall an art historian friend telling me once that a certain school of landscape painting was directly enabled by the introduction of pre-mixed paints in tubes that could be easily carried by the artists to remote locations.
My first suspicious would be a new set of dyes. The first synthetic dye (mauveline, which is even a bit violet!) was discovered in 1856, and sparked a revolution in colors.
> Nine different pigments were found on the painting. Many of the identified colors were modern pigments that became available only late in the 19th century as a result of scientific advances in pigment chemistry. Although similar colors were available in a natural mineral form, they lacked the vivid color of their manufactured counterparts. The use of these new synthetic metallic oxide colors by Monet accounts for the brilliance of his paintings. (https://www.cambridge.org/core/journals/microscopy-and-micro...)
The nine pigments are lead white, vermilion, cadmium yellow, chrome yellow, lead chromate, viridian, emerald green [copper acetoarsenite], cobalt blue, and French ultramarine.
I guess of these, lead white, vermilion, and french ultramarine have been used historically, but the other six were first synthesized in the 19th century. One could imagine that having access to cheap bright colors influenced art...
Maybe one can draw a comparison between the critics of the 1880s complaining about “harsh blue and garish lilac”, and the current complaints about movies being color-graded to teal and orange (“Seriously, I weep for cinema of this dark age. I think twenty years from now people will look at films of this era and say "My God - what were they smoking??!?” ---http://theabyssgazes.blogspot.com/2010/03/teal-and-orange-ho...).
In both cases, the colors are striking and beautiful, or depending on your tastes, cheap and garish.
