I'm not quite sure if this is the same issue, but when I was editing the colors of my Elin pirate mod I had a ton if issues with repacking and when it did repack I had an issue with it in game (the characters were semiseethrough with a static look). I also had a few crashes and after 2 days of getting annoyed with Paint.net I moved onto GIMP. It's similar and free and the magic wand is amazing for selecting and recoloring. I will say that factors that came into play was when I was saving and exporting. You have to be careful that 1 the format is correct (can't remember offhand what I set it on) 2 that you don't select the wrong thing (which was a common occurrence with my mods). Tera can be pretty annoying at times (particularly the older files) and it took me 3 days (without help and getting lost in the black hole referred to as youtube) but I eventually figured it out.
Remember that the format must be in .dds format (I'm sure you know this) but be careful, when you save in paint.net if I recall it saves in paint.net format (xls? idk) Gl!
Remember that the format must be in .dds format (I'm sure you know this) but be careful, when you save in paint.net if I recall it saves in paint.net format (xls? idk) Gl!