What is the proper name for a rainbow effect created by the splitting up of white light?

The splitting of white light into a spectrum of colours is called dispersion.

The splitting of white light (Polychromatic) through a prism shows many colours in a spectrum, this is also known as Monochromatic Light. The colours present would be:

Red, Orange, Yellow, Green, Blue, Indigo and Violet.

The proper name for the rainbow effect created by the splitting of white light is dispersion.

Dispersion occurs when light passes through a medium, like a prism, and is separated into its component colors (the spectrum), ranging from red to violet. This happens because different wavelengths of light are refracted (bent) by different amounts