Depends on the paints you are using so some specific manufacturers (like Golden) can give you some ideas but at the end of the day you are better off doing the hard yards and learning how to do it. Charts give you a hint!
One thing that helps me is cut a small hole in a piece of paper make some test strips. Place your reference down and overlay the paper with the hole in it so to isolate the color you are trying to duplicate. This way the eye doesn’t catch all the surrounding hues.
Next mix what looks as if it is that color. Spray that color on your test strip. Slide the strip in between the reference and the paper with the hole. Allow the reference and test strip to be visible at the same time and compare. This will help you see what to add.
Also keep a color wheel around so you can get an idea what to add.
iOS app True Color gives you the percentage of white blue yellow and red of any color you picked in a picture, I tested a few times and was extremely precise with the paints brands I tested!