If you do not complete your project, you can store your excess paint in an airtight container like a plastic container you would use to store leftover food. Consider wetting a paper towel or sponge and placing it in the bottom of your container, or using a Sta-Wet Palette to keep your paint from drying out.
If you accidentally mix too much black into the blue, have some extra blue paint on hand to even out the ratio.
A good place to start would be mixing Burnt Sienna with Ultramarine Blue. Another possible color combination is Cadmium Orange and Cobalt Blue.
It is a good idea to save some of your blue paint in case you add too much orange and need to adjust the shade by adding blue back into your mixture.
If you accidentally mix too much orange into the blue, have some extra blue paint on hand to even out the ratio.
If you are unhappy with the dried color, go back to your palette and adjust it by adding more blue or purple accordingly.
