> My initial instinct is that finding 12 colors that are visually distinguishable for all users is likely impossible.
Without going to lightness extremes, I agree that this likely isn't possible, at least when trying to accommodate all three types of dichromacy and for small color patch sizes (like those typically used for line and scatter plots). For example, you could take the 10-color accessible palette from work I've published [1] and add black and bright yellow to get twelve colors, but the lightness extremes of adding these colors would result in significantly-different visual weights. Based on a validation survey I conducted, I think even ten colors is pushing the limit of what's reasonable when lightness extremes aren't used.
> could share what colors in the 12-bit palette...are problematic
#9d5 and #4d8 is the color pair I find particularly problematic.
While not completely identical, it looks very similar (I also only have strong protanomaly, not complete protanopia, so I wouldn't expect it to look identical).
Color-vision deficiency simulations collapse colors along the confusion lines, but this can be done multiple ways. These different mapping will all look the same (and identical to the original) to a dichromat but will appear different, with different perceptual differences between colors, to a color-normal individual. Simulating in a way that accurately portrays perceived color distances is still an open research problem.
Please don't use rainbow-type palettes, as they generally have poor accessibility for colorblind individuals. With my red deficiency, the middle two colors in this palette look virtually identical.
I wrote a simple web-based night sky viewer a while ago [1], which renders the 750 brightest stars from coordinates in a data file (along with the moon). It uses D3.js to do fully client-side SVG-based rendering for interactive use, but it could be simplified to render server side to an SVG file. I think the main complication is that by adding stars, a projection needs to be decided on, and you'd need to consider the aspect ratio of the browser window.
Without going to lightness extremes, I agree that this likely isn't possible, at least when trying to accommodate all three types of dichromacy and for small color patch sizes (like those typically used for line and scatter plots). For example, you could take the 10-color accessible palette from work I've published [1] and add black and bright yellow to get twelve colors, but the lightness extremes of adding these colors would result in significantly-different visual weights. Based on a validation survey I conducted, I think even ten colors is pushing the limit of what's reasonable when lightness extremes aren't used.
> could share what colors in the 12-bit palette...are problematic
#9d5 and #4d8 is the color pair I find particularly problematic.
[1] https://arxiv.org/abs/2107.02270