How do I replace Oblivion textures using Paint.NET?

I just started using paint.NET to edit textures for The Elder Scrolls 4: Oblivion. I opened the white monk shirt texture and changed it to white and black then i set the brightness down until i got the color i wanted. I didn't replace the file i just saved it in my custom textures file using default settings. Then using Nifskope i replaced the shirt texture with my custom one, then saved it in my custom Nifs file. I went to TES construction set and opened up the piece of armor i made and replaced the nif file with my custom Nif (before editing the texture the file was identical to the original white monk robe). i started up oblivion with my mod activated, and loaded my game. When i looked at myself in the journal every part that would have been changed by the edited texture was invisible, the same happened in 3rd person, everything else was normal however. If someone using paint.NET has experienced this problem before and figured out how to fix it could they please help me out and tell me what you did?