Complementary colours always juxtapose one cool colour with a warm colour. Reds, oranges and yellows are the warm colours, while blues, greens, and purples are the cool colours.
In the context of light, complementary colours result from the additive mixing of wavelengths of light. When all three primary colours are mixed they produce white.
In the context of paints and inks, complementary colours result from the subtractive colour mixing of pigments. When all three primary colours are mixed they produce black.
The mixing of pigments such as powder colours is more complex than mixing known wavelengths of light. When all three primary colours (cyan/magenta/yellow inks or red/yellow/blue powder colours) are mixed they often produce muddy brown or purple colours.