1. The 12 colour RYB (or artistic) colour wheel
This colour wheel or colour circle is one of the basic tools for combining colors.
This example shows the 12 colour RYB (red, yellow, blue) colour model.

2. Colour wheel Here are others
Source:
By J. Arthur H. Hatt (The Colorist) [Public domain], via Wikimedia Commons

3. Make a simple Red:Yellow:Blue colour wheel
Mixing the 3 primary colours creates the secondary colours, which mix to create the tertiary colours, as so forth
Primary Colours (blue/yellow/red) - these can't be made by mixing others together
Secondary Colours (purple/green/orange) can be made by mixing the primary colours
Tertiary Colours from mixing primary and secondary colours

4. Complementary colours
blue
Colours opposite each other on the colour wheel are known as complementary colours
Green
Purple
Red
Green
blue
Orange
Yellow
Purple
Yellow
Red
Orange
Red/Yellow/Blue (RYB) Colour Wheel

5. Complementary colours
Complementary colour schemes are highly contrasting and vibrant
Useful for drawing attention or for making things stand out
These combinations can sometimes be jarring - complimentary colours are often bad for text
Red on Green
Green on Red

6. Complementary colours
The complementary colours of the 3 primary colours:
yellow
red
blue
are found from mixing the other two to form secondary colours:
red + blue = purple
blue + yellow = green
red + yellow = orange

7. Complementary colours
Complementary colour schemes are visually very high contrast, but can sometimes be jarring

8. Complementary colours
The shadow of an object will also contain its complementary colour, for example the shadow of a red apple will contain green
If you look at a colour for long enough then look at a white background, you may see the complimentary colour for a second
Look at the following coloured slides then look at the white - do you see the complimentary colour for a split second when you look at the white background?

13. Triadic colours
blue
Triadic colour schemes use colours that are evenly spaced around the colour wheel
Triadic colour schemes are quite vibrant
Green
Purple
Yellow
Red
Yellow
Blue
Red
Orange
Green
Purple
Orange

14. Triadic colours
To use a triadic harmony successfully, the colours should be carefully balanced - let one color dominate and use the two others for accent/emphasis
Yellow
Blue
Red
Green
Purple
Orange

15. Analogous colours
blue
Analogous colours are next to each other on the colour wheel
They usually match to create serene, natural-looking and comfortable designs.
Often harmonious and pleasing to the eye
Green
Purple
Yellow
Red
Orange

16. Analogous colours
Make sure you have enough contrast when choosing an analogous colour scheme
Choose one colour to dominate, a second to support. The third colour is used (along with black, white or gray) as an accent/emphasis

17. Split-complementary colours
Split-complementary colours are the 2 colours adjacent to the complementary colour
Split-complementary colours are contrasting, but not not as vibrant as complementary colours
Split-complementary colours are safer and easier to use than complemetary colours

18. Rectangle (tetradic) and Square colours
The rectangle (tetradic) uses four colours arranged into two complementary pairs.
The tetradic color scheme works best if you let one color be dominant with a balance of warm and cool colors

19. Square colours
The square color scheme is similar to the rectangle, but with all four colors spaced evenly around the color circle.