A color wheel or color circle is an abstract illustrative organization of color hues around a circle, which shows the relationships between primary colors, secondary colors, tertiary colors, and complementary colors.

They key takeaway from your initial learning of the color wheel is to remember:

Primary Colors (the red, blue, yellow)

How to mix the Secondary colors (orange, green, purple) 

Pairs of Complementary colors, which are opposite of each other on the wheel

The colors on the first half (red, yellow, orange) are typically your warm colors and are used for objects that are closer to the light source. Colors on the other half (blue, purple, green) are your cool colors. Colors are used for objects further away from the light source or in shadow.

Essentially, colors diagonal from each other on the color wheel, strips the color out of each other. Meaning to tone down, or create a grey shadow a color, you add the color that is diagonal to it on the wheel. 

For example, if I’m painting a red rose, for the shadow of the rose I would add green to the red to make a dark grey red. If I’m painting a banana, for the shadow parts, I would add purple to yellow to create a yellow grey.

Here is a quick cheat sheet on how to mix the colors on the color wheel and how to mix other commonly used colors as well. This cheat sheet can come in very handy when you are painting. Even if you aren’t mixing these particular colors, it’s a good reminder of how different colors mix with each other.

Red & Blue = Violet

Red & Yellow = Orange

Blue & Yellow = Green

Brown = is a type of Orange or Red

In reference to the color wheel:

Red & Green = Grey Red or Grey Green

Yellow & Violet = Grey Yellow or Grey Violet 

Orange & Blue = Grey Orange or Grey Blue

Tips on how to mix colors:

Keep in mind the color that you are trying to mix, whether it is either a primary color or secondary color 

Refer to the primary color combinations to mix if it’s a secondary color 

Then refer to its complementary color on the wheel to tone it down

You can add white to lighten it, but that usually flattens it and makes it chalky 

You can darken it with a dark color (black, paynes grey, violet, blue, alizarin crimson)

You can add a warm tone to warm it up, this typically lightens it at the same time