So starting out with traditional mediums I have always struggled with the color palette on most of the digital paint programs we use today. I think they're great as far "picking" colors but in reference to working with real paint vs digital there isn't a real structure on selecting and mixing. For instance you wouldn't use solid black for traditional paintings or mix white in with your paint to lighten a color, you would use other colors to mix to get better results. I wont get into color mixing, you can find a wealth of information on this on the net.
The point I'm trying to make is color picking has always been kind of a pain for me, even if using a digital color palette with dabs of colors on a separate file it just isn't the same. I did some image searches for color palettes and found an image on a color palette of real paint and thought why not just use that as a color palette instead of trying to build a digital color palette based on it. I've been testing it and it actually works quite well for me because the natural light on the paint also provides an added bonus of highlights and darks for that color.
This works really well with programs like Painter and Artrage that "mimic" the color blending and mixing too. I know this isn't groundbreaking but I'm not sure why I haven't done this before.
If you're interested in trying the same image as a color palette I found it from the following blog. [link]