I always had to be careful when creating paint kits for my numerous models and I would inevitably have to make a paint kit for Photoshop users and one for 'the rest'. I make use of layer 'folders' a lot (i.e. a lot of layers inside a folder for that particular paint scheme or common things like rivet layers, panel lines, dirt, etc.) and free image editors like GIMP, Irfanview, MSPaint etc. cannot handle Photoshop layer folders at all so I would have to pull all the layers out of folders so that there was just a big long list of layers with no organization at all.