I have a color blind designer friend who uses a lot of widgets like this to work. When you can’t see exact shade you need to be fairly careful that colors actually look good together. But they aren’t generally useful to him unless they output panatone or hex color codes or something. Since he can’t match the colors accurately by sight, and needs to replicate things in other software.
It depends on the color system.
It’s primary in RGB (addative light). And secondary in CMYK (subtractive). And there are alternate sets of colors used in both models.
