yes, this is something made on purpose, there was some kind of debate about the subject. The basic solution to what you say is to leave the switch in the side (right) of Mission Skin, so nothing is changed (but if you used that plane with a differnet skin selected by yourself in the past it will be applied by the stock game to you). So I introduced the option of "Player Skin", and basically two different behaviors were possible when specifying skins:
-The change affects all the members of your flight, so if you change the skin all your flying partners will look similar.
-The change affects only your plane, the eventual 3 other members of the flight continue to have the one of the mission.
I adopted the first one, because the big problem of the second one, I saw it many times, and that is the reason why I took that decision, perhaps you were flying with a blue skin and all the other members of your flight were with a silver skin, and just tell me if it is not worst than repeating numbers, the differences could be too extreme.
The problem is that there isn't more space to place another switch to select Skin to All or only to Player or another combobox. It's difficult to solve all the eventual different needs.
If someone proposes something that could solve all the requirements I can implement it, but it isn't so easy.