If you use three good true primary colors like Cadmium Yellow Light, Napthal crimson, and Thalo Blue you can mix many wonderful colors. But your blue and red to make purple will not be vibrant because Thalo Blue leans a little to the green side on the color wheel. (When red and green are mixed they neutralize each other because they have opposite characteristics. That is why they are called contrasting or complimentary colors.) So you will end up with a dark dull purplish color instead of a vibrant purple. This can be a good thing if it is what you desire.
With the above palette you can get orange, but not as brilliant as if you use Cadmium Red Medium (or Cad Red Light) mixed into your yellow. But even then Cadmium Yellow Light leans to the green side a little. So you can see the need for Cadmium Yellow Medium. This leans more to the red side and makes a stronger more vibrant orange.It is hard to find perfect primary colors. they always lean to one side or the other on the color wheel. To solve this problem I use a split primary palette.
For my blues I like Ultramarine Blue (a true blue that leans to the red side of the color wheel a little) and Thalo Blue (which leans to the green side).
Reds: Napthal Crimson (leans slightly toward purple) and Cadmium Red Medium (leans toward orange),Yellows: Cadmium Yellow Light (leans to the green side), and Cadmium Yellow Medium (leans to the orange side).
Buy a color wheel and put it in a plastic sleeve and place your colors on it it to see where they fall. When you are finished you can wipe the sleeve off or throw it away and use a new one next time.If I want to make a bright green I will use Thalo Blue mixed with yellow. Thalo is powerful and makes amazing greens. On the other side, when Thalo Blue is mixed with Napthal Crimson it makes almost a black color. If I want a violet that is not muddy I will use the Ultramarine Blue and the Napthal Crimson. If I want a mauve I will mix the Ultramarine with the Cadmium Red instead. Of course using whites for tints gives you all kinds of values to choose from.
I don't really need Burnt Umber because I can mix up an orange and add a little Ultramarine Blue and have a nice range of browns. But I love this warm brown and often use it for dulling my greens or mixing with blue and white for a nice gray.I have also begun to use Dioxazine Purple. It is dark and when White is added to it it is very vibrant. Even more so than I can make with primaries leaning toward purple. Dioxazine Purple is also great for dark shadows, add a little of it to green for deep dark shadows, or add a little orange for warm shadows.
Here is an example of these colors and how they can be used to make new colors:
Ultramarine Blue with burnt umber and white are at the top left. Thalo Blue top middle. Cad yellow light is next to Thalo blue. Ultramarine Blue is just below the Cad Yellow Light.
Napthol Crimson and Thalo Blue make the dark area just above the red on the left bottom. Cad Red Medium and Cad Yellow Medium make the orange on the right. Some of the complements are mixed in the middle with white all around.
(Cadmiums come in hues, which are even more brilliant than the regular cadmiums. I also use them because they are less expensive and less of a risk to the artist and the environment.)
Here are some more ideas for mixing your own colors: Try Alizerine Crimson as one of your reds: Prussian blue is a nice dark blue to try out; Hansa Yellow is a good yellow also; If you don't like mixing your own greens, add permanent green deep to your palette, just be careful not to paint with it straight from the tube too often as it can take over! Mix other colors into it for variations. Black can be beautiful in your paintings, especially if you use it with other colors. use it sparingly until you are confident with it.
Feel free to email me if this is not making sense! smile. I will try to help if I can.