Why don't you show a picture of such a color?
TLDR: JPG files and computer displays cannot differentiate these, so it's not possible to do what you ask.
The human eye has cones that pick up red, green, and blue, although they pick up wide bands: red picks up deep red down to (almost) infrared, and all the way up into oranges and yellow. Similarly green picks up more than green, and blue more than just blue. We also have rods that pick up brightness (i.e. black & white vision), but the rods aren't interesting to this.
When we see cyan light, it's triggering both green and blue cones. Our brain mixes that to perceive cyan.
When we see purple, it's triggering both blue and red. Our brain perceives purple.
When we see violet (the kind I'm looking for, at wavelengths shorter than blue), the blue cones pick it up. But, curiously, the red cones also pick it up violet. The end result is that as far as human vision is concerned, violet and purple are the same thing: red and blue. And artist's color wheel will tell you then violet is a different shade than purple. But that's basically the same as arguing about reddish purples or blueish purples.
As for computer displays: they emit red, green, and blue of specific colors. It's a specific blue. But the mixing works similarly: while a computer cannot directly produce cyan: it instead turns on some blue, and turns on some green, and our brain ends up getting the same signals as if we were really seeing light of the wavelength for cyan.
A computer display cannot emit a true violet. Not to mention that a JPG file with red, green, and blue channels cannot represent a true violet, either. So instead a JPG to show violet is recording red and blue of a certain mix, and the display is showing red and blue of a certain mix, and our brain perceives what it is intended to perceive.
To be clear, I'm looking for an ink with an actual violet dye. And not an ink with blue and red dyes that make me perceive the same thing. I'm sure this is a niche request with little practical value, but I'm hoping somebody remembers that such an ink was mentioned way back when.
Edited by XYZZY, 12 June 2019 - 06:46.