The truth is probably that there is no ‘true’ color because the rotoscoping in the OT was not very good (especially ANH). Whatever color it is ‘supposed to be’ is probably whatever it was in the PT or TFA.
This is one of the things that has always bugged me about all the updates of the OT over the years. If you are going to go to all the effort of adding to/changing the films, erase the old rotoscoping and fix it proper!