Skin shows in parts picker but won't actually apply?

I decided to try making a skin again after giving up, i've created the skin and when i load it into the mods folder, it appears to load successfully but when i try applying it, i just get a blank van. what's weirder is that when i go to the debug screen, there are no errors relating to the skin file, only about actions that aren't detected (such as the dumper bed on the semi truck)