The color circle, or color wheel, is an orderly and circular representation of the colors according to their hue or tone, where the primary colors and their derivatives are represented. Its use is compatible with both subtractive color models and additive models. Wikipedia
Colour Mixing Chart - Basic Color Combinations
These are some basic Colour Mixing Chart combinations suggested to show the basic how-to painting for the lighting and shading of the colors marked "Initial". It is recommended to introduce intermediate steps combining both colors (Lights + Initial or Initial + Shadows) at 50% or in another proportion.
Combinations for Painting NMM (NonMetallic Metal)
These are suggested color combinations for painting some "non-metallic metal" effects. These are only suggestions and it is recommended to combine the colors according to the surface to be painted and the desired effect.