Underneath you can find all colours of the GS and GSA during its lifetime. Names of the colours are in French. For your convienance I translated them in some common languages.
The official colour code of the colour is listed next to the name. Use this code when ordering paint.
When ordering paint, find the colour code on your car to make sure you match the colour and thus order the right colour.
Or alternatively have an paint shop measure the paint, so the influence of the elements during the years can be taken into account aswell.