The next to the last section of the OFF forums tells you how to make skins. However, it is not really easy and takes some work and special programs to open and view the skins that are already made (basically you need a program that will view dds files, like Irfan view, which is free). To paint skins you will need a dds to bmp converter like DXTbmp which is also free and there should be a link in the other section of the forum. The skins are located in the skins folder which is found in
C:\OBDSoftware\CFSWW1 Over Flanders Fields\campaigns\CampaignData\skins
If you go to the download section of this forum you will be able to find custom skins for all of the 94th Showbird Spads that were used after the war. It is a little early yet to find custom skins for the N28s.
Beard