This technique is crazy! It allows to both:
You actually see discrete peaks at different minute counts on the other end.
- separate gaseous mixtures
- identify gaseous compounds
It is based on how much the gas interacts with the column.
Detection is usually done burning the sample to ionize it when it comes out, and then you measure the current produced.
The procedure remind you a bit of gel electrophoreses, except that it is in gaseous phase.
The name makes absolutely no sense in modern terms, as nor colours nor light are used directly in the measurements. It is purely historical.