Look around your living room. Most of the colors you see in the sofa, the rugs, the ceiling, just about everything is neutral, or at least somewhat neutralized. The exceptions are usually manufactured objects, like throw pillows, or art on the walls.
In nature, it's the same thing; the color of the majority of what we see involves all three primaries.
For homework, find two neutral-colored objects, one warm and one relatively cool. Using one red, one yellow, and one blue, combine the colors to match your objects as nearly as you can. Make a patch of your colors on paper. Take note of the colors you used.
Now choose a different red, yellow and blue and match the objects again.
We'll spend some time next week laying out your palettes, so bring all your colors.