The skin in "sapphire" folder is for the official version, as well as the_meco's standard and s1 versions of Cobra. It is numbered 22.
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\content\cars\shelby_cobra_427sc\skins
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\content\cars\shelby_cobra\skins
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\content\cars\shelby_cobra_s1\skins
The other skin in "sapphire_competition" folder is specially made for the_meco's competition version of Cobra, which has the number "24" on its left side and right side.
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\content\cars\shelby_cobra_competition
If you would like to switch the skin appearance between the two versions, you need to not only copy and paste the files, but also rename the file "CobraBody.dds" and "CobraBodyCompetition.dds" from one to another.