I take a bunch of different approaches so the short answer is "Yes" but I'll try get a little more in depth.

I mostly use something akin to a "imitate real brushwork" algorithm, but it's more a "mess with the code until it looks right to me" algorithm.

> Do you do color change by swishing the brush in water?

Sort of, this aspect of definitely has some physical bugs (flooding my work area occasionally) but I am using an automated water pot that works using a pythagorean siphon and is controlled using the coolant flood commands in GRBL (used to cool bits when cutting with a CNC ordinarily)

> Ooo, does it mix colors?

This is what I'm currently working on, but it's very much a non-trivial thing to solve. Luckily you don't have to be precise to make good art, there's a lot of opportunity for happy accidents.

self promo: While I haven't been very good at producing compelling media about my plotter, I do have a patreon where for $7/mo I mail you a postcard-sized plot every month demonstrating whatever thing I'm working on at the moment. https://www.patreon.com/thot_experiment

here are a few examples of last month's plots, these are colored by hand https://thiic.cc/heavy/bb_plot.jpg https://thiic.cc/heavy/crank_plot.jpg https://thiic.cc/heavy/pedal_plot.jpg

and here's a few that are pure robot https://thiic.cc/heavy/abstract_plot.jpg https://thiic.cc/heavy/other_plots.jpg