I have flown my first 18 missions with JASTA 3, with the default aircraft skin (creamy white).

I then went into the flight setup where you can adjust the loadout for the upcoming mission and then selected my plane to have the JASTA 3 (1916) paintjob, which worked for that mission as I was flying solo...

Since then, each time I have tried to change to the same paintjob it continues to show the cream/white in the actual mission...I have selected and then deselected several times but still the plane skin remains in the mission... anyone else had the same issue?

I don't have the add-on skin pack btw... although I am sick of the plain white of my HALBERSTADT so if anyone has a fix I am all ears...

Sounds like an odd one, maybe send the WOFF logs from a mission where the you select a skin and it doesn't work (see last page of the WOFF FAQ on our website Download page) to support.
http://www.overflandersfields.com/Downloads/FAQ%20WOFF.pdf

Also make a note of the squadron, date, and the exact skin name you choose.

Are you getting the pop-up window asking you to confirm the skin change whenever you select a new one? It should have a checkmark and an 'X' to confirm.

Its strange, it worked the first time I tried it although not anytime thereafter.

I am flying with 'Jasta 3' and it is around Sept' 1916 in my Campaign so I selected the 'Jasta 3' 1916 paint scheme from the list.

It then says to confirm like you have mentioned, although when I move the mouse cursor down to the menu options the screen flicks to the campaign map... I then click to start he mission (head to field) of whatever is says, however my HALBERSTADT still has the generic cream/white canvas in the mission.

I will try it again this afternoon to see if it happens again.

If you move the mouse cursor back down to the bottom bar, in the campaign menus, it will exit the current screen you're on (Loadout screen for example) so if you haven't confirmed the selection, it probably didn't work since you exited before doing so.

It took me a few head scratches to figure out why some of the campaign menus would exit back to the main one with the map, when I first started playing. Eventually figured out that moving the mouse down below would do that. It's nice not having to click the 'Done' button all those extra times but can be confusing at first until you know what's up.

I selected the JASTA 3 - 1916 skin and then clicked the 'TICK' to confirm, however there is no other way to get out of the briefing screen other than moving the cursor down to the bottom panel to select head to field / proceed to mission...

I don't understand it, it worked the first time I tried it and yet there seems to have been a glitch that wont allow aircraft skins to work in the mission......bloody frustrating!