In theory, with just the primary colors (red, yellow and blue) you can make any color at all. To move the color you have closer to the color you want, you just need to add some red, some yellow or some blue. In fact, this usually is how it works, but the theory is based on combining light rather than paint, and most paints as they come from the tube are not single, pure colors. As you saw when we were laying out palettes in class, some yellows are cooler than others, and some warmer. Alizarine crimson is a slightly purplish red, while cadmium red light tends toward orange. We call them both red, but one might be a better choice than the other if you are trying to match the color of a particular bunch of grapes. To me, this is a good thing. Imagine if your palette had only three color wells.
Please read the following twice before you get to work:
For homework, look through a magazine for patches of solid color an inch or more square. Let some of them be complicated colors, like an eggplant, or a paper bag. Greys are challenging (fun). Cut them out and paste them to a sheet of white paper.
Now choose one red, one yellow and one blue. Only one of each, for now. Using just these primaries, make the nearest match you can to the color patches. As you finish each one, paint a stroke of the color next to the cut-out square it matches. Take some care to get the value right, too. Write down the names of the primaries you used.
Next, choose a different set of primaries and try the same matches again.
When you've finished, try mixing the darkest color you can from each set of primaries. Remember, the paint can be pretty thick and still be slightly transparent. If your dark looks shiny even after it's dry, add a tiny bit more water to the mix.
A couple of questions to ponder:
How important is it to get the paint color to exactly match the subject?
Can profound darks be warm or cool?