I'm not familiar with an app showing spectra of pigments as used in painting, etc. Some high-end printers (plotters) incorporate spectrophotometers to measure properties of colors, but that's a highly controlled use of colorants.

In contrast, a painter can use a color in thick or thin layers, mixed with white, or clear medium, among other variations. And pigments can work differently in oil vs. acrylic vs. watercolor media. The spectrophotometric properties of a pigment change depending on usage so the information gleaned from measurement would probably not be that useful.

OTOH some manufacturers offer visual color mixing guides that can be helpful to artists. Here's one I've used from time to time: https://goldenartistcolors.com/mixer/acrylic?tab=color-syste...

This offers matching artists colors to RGB or CMYK specifications.