GW was always a free colour for normal Renaults. It used to be £150 option for RS models although I'm sure it's more now.
Pretty sure glacier white was on the rs range was free, pearl white was the £1200 option in the id paint range
wrong. It was initially. Once it became popular it became a RenaultSport ID paint and they started charging £150. This was around 09/10
Glacier white was available for Monaco GP versions of Megane and Laguna coupe. I am not sure about World Series of Renault Megane. Probably it is not available anymore, like Venetian Red, lovely paint I had on my Laguna mk3 Initiale Paris.