So I've just run into this issue for the 2nd time. When I open my mod (truck) in the editor all the textures are fine. When I load the game and go to Proving Grounds and spawn the truck from the UNPUBLISHED files the textures are fine. If I load the PUBLISHED version of the truck in Proving Grounds or any other map, the textures are NOT fine. My black bumpers and rims are green instead. On inspection of the workshop .zip file, I find that there are 2 files with identical names: 1 is the actual black texture file that SHOULD be applied, the other is a washed out gradient and appears to be the texture that is actually being applied to the bumpers/rims. Deleting either of the duplicated files (or both) from the zip results in white "missing texture" bumpers/rims. This is the exact issue I had previously except it was the body texture instead of the bumpers/rims. I edited the gradient texture in Photoshop and changed it to a straight black texture and added it back into the zip and it resolved the issue on a purely visual level (there are still 2 identically named files in the zip) but this doesn't fix the issue for anyone else who doesn't modify the files on their end. So it's the texture conversion/publishing process that's to blame as far as I can tell. Has anyone else run into this issue? If so, did you manage to fix it and how?
That would be my guess as well, and yes I'm 100% certain the filenames are identical because I had the same thought "Windows doesn't allow 2 files to have the same name, so how is this happening??" It only applies in the archived/zip though, because if you extract the zip it prompts you about the filenames (file_blah.dds exists, overwrite?)
EDIT: Just had a thought, if it's relevant to texture compression why is the "new" texture (the gradient) almost 5x the file size of the original texture file? Also it behaves as if the 2 files are somehow linked because if I simply delete the duplicate/gradient texture from the zip, it breaks the texture in-game even though there is still a texture in the zip with that exact same filename...
cue X-Files/illuminati music...
So I've confirmed, with some help from @FearWheels that the published .zip file does in fcat contain 2 identically named files. The proof's in the pictures. Ignore the file sizes for the relevant files (kdnri5s0_d_a.dds) in the screenshot below since, as stated in the OP, I've already modified the gradient file locally so that at least in MY game my bumpers/rims are black instead of green...
Before uploading it's actually a single texture file "black1__d_a.dds"
It's not strictly "duplicated" so much as it's replaced and duplicated simultaneously...? I know that sounds confusing, but it's adding a texture file with the same name as an existing texture file, but the one that's getting added only has the same name (once published) as the original texture file, it's not a duplicate as far as it's contents are concerned.
Original texture file open in Photoshop, note the RGB values.
Shows as black in the editor, as it should.
This is the original texture AFTER being published, from the Workshop .zip file. Again, note the RGB values. This file is 2KB in size (compressed).
This is the new/duplicate file AFTER being published, also from the Workshop .zip file. Once again, note the RGB values. THIS file is 11KB in size (compressed).
Here's a screenshot of the truck loaded in the Proving Grounds from the published files. Note the GREEN bumper and rims.
And here's one of the same truck loaded in the Proving Grounds from the UNPUBLISHED files. Note the BLACK bumper and rims.
do you have another texture that contains the word "black"?
also try naming the texture something else (something random, letters) and try uploading again.
there's a problem with renaming when you have multiple files of the same name, i've had a similar problem when i had meshes/classes .XML files and textures with the same name (i.e. toolbox.xml and toolbox__d_a.dds)