When starting a new project that involves painting, if you are not sure what colors will be needed, always be sure you have all of the primary colors. Anything else can be mixed from there. As far as tones and values go, pick medium tones, because these can easily be made either lighter or darker. Red, blue, and yellow, plus black and white for changing shades, are all you really need.
Mixing from primary colors
It should be common knowledge that any color you need can be mixed from the primary colors. Although a veritable rainbow of colors are now available, especially with regard to craft paints, it is actually quite fun to mix them yourself. You can come up with unique shades this way, and emulate harder to find colors as well.
However, if you do go this route, I would suggest that you mix a large enough quantity in the process to finish the entire project, so that you will not be having to make colors later. This will save you loads of time trying to rediscover that perfect shade of cobalt blue or leaf green later on.
Lighter and darker shades made easy
This one should probably be a “no brainer” as well, but you would be surprised at the artists and craftspeople who are hesitant to try it. If you want a lighter shade, add white. If you want a darker shade, add black. Yes, it really is that simple.
However, there is a trick to this. It involves patience and carrying through with what you start. Once you begin mixing a shade, you must be patient enough to be sure it is mixed thoroughly, because this can change the color tint.
As mentioned with regard to mixing colors in general, you must also mix enough to begin with to complete the entire project. This can be especially important when mixing variant shades.
When in doubt as to what is needed for any painting job you undertake, always be sure you have plenty of all the primary colors (red, yellow, and blue) on hand. You will also need plenty of black and white for mixing different shades. Containers and tools for mixing and storage will also be invaluable in this process.
Source: Over 30 years as an artist, crafts-person, and trainer of others in these fields as well.