There are seven colors in the visible light spectrum: red, orange, yellow, green, blue, indigo, and violet (ROY G BIV).
When all seven colors of light combine they produce white light. The colors of objects appear the way they do because of how they interact with light. When an object appears red, it absorbs every color of visible light EXCEPT red, which it reflects. Thus, how light is absorbed and reflected in relation to these objects is what determines their color.