You must be an artist - thanks for the explanation to a geek!!
You don't need to be a trained artist for much of this.
A five year old who has played with fingerpaints will quickly learn that mixing seven different color paints will not result in super bright rainbows.
Even the conceptual difference between additive and subtractive color dates back to the mid 19th century.
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Various art programs will do this as well. also can emulate paper texture, etc.
Well, whatever this artist used for this image, it wasn't one of those programs for sure.
Can you name a few? I'd be interested in trying them myself.
As for simulating paper texture, that's old hat. Digital compositing tools twenty-five years ago simulated film grain.
In the OP's posted image, there is no paper texture. That's another big clue that this image is digital. Watercolor works best with uncoated and textured paper than can hang onto the pigment molecules.
Hot press, cold press, texture amount, cotton rag percentage, sizing amount. Those used to be criteria that artists used. For Watercolor Painting A, it might be Fabriano paper ____; for Watercolor Painting B, it might be Arches paper _____. Because of the nature of paper production, the two sides were occasionally not the same.
Fine paper usually has a "top" side and a "bottom" side, typically identified by the watermark or manufacturer's embossed logo (*cough* Fabriano *cough*). Sometimes the sizing was only applied to one surface.
Sometimes the "wrong" side would provide better results for a given project.
One company's hot press paper might be closer to another company's cold press paper. There was never just one "watercolor paper" [sic]. Most of the watercolor artists who cared about such details are dead.
This is partially why painters still create works on fabric canvas (cotton, linen, etc.): so the pigment vehicle will adhere to a rough surface.