What causes the different colors in the color spectrum?
White light is a mixture of different color; a prism or similar device that produces a spectrum simply separates these colors.
the difference is that white light is a mixture of the seven spectrum colors but when refracted (separated by a transparent object) it splits again into seven colors striking at different angles that's why they look like one.one color above others.so the difference is that spectrum is a number of split colors striking at different angles but white light is the mixture of those colors.
I think you are asking about visible light spectrum as that is also called color spectrum.Their are mainly seven colors in this spectrum-Violet,Indigo,Blue,Green,Yellow,Orange and Red. So, the fourth color is GREEN. A easy technique to remember this seven colors is VIBGYOR,where each capital letters represent the first letter of the colors.