The effect of the glass prism is only to distinguish the seven colours of the 

The glass prism's effect is limited to separating the seven colours of white light. If a beam of white light is passed through a triangular glass prism, the white light splits to form a band of seven colours on a white screen.

The band of seven colours formed on a white screen, when a beam of white light is passed through a glass prism, is called spectrum of white light. The seven colours of the spectrum are Red, Orange, Yellow, Green, Blue, Indigo, and Violet.