Hope I'm not bugging you guys with all the questions but the Fuji Ultra Poly NOCP Rod Building Thread claims that you don't need color preserver has anyone had any experience with it? Would it hurt to put it on anyways?

Yes their claim is correct. No it will not hurt, it will help it maintain the color even more so. But keep in mind if you are going to go through the trouble of applying CP anyways, nylon thread will yield more brilliant results with its sheen.

I put some CP on a decal to seal the edges and mistakenly got some on some white NCP thread nearby. It was noticeable (under examination) when I put the epoxy on. It wasn't the same as putting epoxy on white nylon, but it did darken slightly except where the CP had touched the thread. Not a huge concern as the area was small beyond notice to the casual eye, and I only build for me right now.

What about when using Permagloss on white NOCP thread? Better not to use CP?

Oops that's a tough one. I've never used PG over CP. I know it's supposed to be "hot" and even melt some paints. Don't know what it'd do to CP. You could always test a wrap on a wooden dowel. That's what I do because I don't have a ton of scrap laying around.

It won't hurt any of the popular color preservers.

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But will the CP add a shade of amber to the mix after time in the sun? Or will it help make the white thread more opaque?

It will definitely help make it more opaque.