This depends a bit on what you are looking for. The library documentation is supposed to guide you to a practical starting point, but it's still quite light on the theoretical parts. I haven't really collected any specific beginner material, so this may still be a bit technical. There's a ton of info about the basics, with varying levels of detail.

Assuming you are starting from almost nothing, I would recommend getting familiar with what RGB is and how its components relate. This is the format most images are encoded in and most devices and software use. The Wikipedia page is quite thorough, so no need to read all of it: https://en.wikipedia.org/wiki/RGB_color_model

Next, it's good to know there are other models. HSV and HSL tend to be used in color pickers (a bit more intuitive than RGB), so you have probably interacted with them at some point. Again, the Wikipedia page may be a good source: https://en.wikipedia.org/wiki/HSL_and_HSV

That's often good enough for producing colors and reading or writing images. If you want to go more into editing, it's good to know that you will need to massage the values you get from the images. They usually don't represent the actual light intensities, so they have to be made linear. Palette offers functions for it and represents it in the type system. This video is a slightly simplified explanation of the problem (when it mentions the square root, it's an approximation): https://youtu.be/LKnqECcg6Gw

At some point, you will realize that neither linear nor non-linear RGB is the universal answer to good looking colors. They are used in different situations. There is another category of color models/spaces that are called "perceptually uniform", meaning that they try to simulate or predict how we actually experience the colors and relate it to the numbers in the computer. This page shows the problem and introduces one of those models: https://bottosson.github.io/posts/colorwrong

I can probably provide more sources if you have any specific things you want to read about, but this is a start.