- Undercoat color
- Number of coats
- Gloss Level
- Size of colored area
- Surrounding Colour
- Combination of tinters used by each brand. (Different tinters can make colours metameric)
- Light Source (Incandescent, D65, LED, Fluorescent)
- Monitor Color Space (sRGB, DCI-P3)
- Color Space / Model used for conversion (Lab, Luv, Lch)
- Colour Difference dE Model Used (CIE76, CMC, CIE00)
- Precision and spectral range of the spectrophotometer used.
Etc
With most paints, the medium used can affect color, as well as aging. I used to use Ph Martin watercolor dyes, and they were notorious for fading after a relatively short time. The illustrations that I colored with them, are now monochrome. I’m sure they’re better, now. Pigment science has come a long way. Acrylic was always a lot longer-lasting.
Also, context matters. Our perception changes, based on surrounding colors. There’s a bunch of optical illusions that leverage this.
But I think this is kind of a cool project.