What happens when you shine light through a diffraction grating?

If it's white light, you get a rainbow

Two Prism Rainbows

If it's a red or a green laser, you get a red or green diffraction pattern

Dots of colored light
Lines of Colored Light

If it's a multispectral laser like the Argon laser in Chamberlin, you get the visible colors that make up the beam

Dots of blue light
Blue Lines of Light