Terracotta is a warm reddish-orange colour named for the style of clay firing that produces pottery of this colour. The word means "fired earth," and the colour adds a natural warmth to a room when it is used on walls. Terracotta is also used in artistic painting. Because terracotta is a complex colour with brown undertones, it may take some mixing before you get the shade you want. However, many two-color combinations produce terracotta.
Red and orange
The simplest way of mixing terracotta is to use red and orange. However, you should try for a combination of red and orange that won't end up too bright, or you will end up with red-orange rather than terracotta. Try using a cool red, such as burgundy, with a warm orange, or a cool orange with a warm red, such as alizarin crimson.
Light brown and red
You can also create terracotta by mixing a warm light brown with red. Several light brown pigments are available in acrylic and oil paints, as well as home interior paints. Try combining burnt sienna or raw sienna with a medium red. Mix gradually until you get the colour you want.
Red violet and yellow
Yellow and violet are what is known as complementary colours. Situated opposite each other on the colour wheel, they create a neutral grey when equal amounts are mixed together. Using red violet instead of true violet, though, will yield colour more orange than grey -- just the colour of terracotta. Play with the ratios to find the right colour for you.
Bright green and red
If you want a reddish, muted shade of terracotta, mix a bright green, such as a grass green, with red. Like yellow and violet, green and red are complementary colours, and will create a greyish brown when mixed together in equal parts. The brightness of the green will help the red retain its basic colour, but it will give the new colour that earthy tone associated with terracotta.
Orange and black
You can create a colour that approximates terracotta by mixing orange with black. Unlike other combinations, which require more or less equal amounts of paint, this one requires that you be very sparing with one of the colours. It is easy to add too much black and end up with a colour that is unusable. Add a little bit of black at a time and mix it thoroughly into the orange before adding more.