How do you minimize the overlapped edges showing when using Coverite, Solartex, Oratex, or any of the fabric coverings?

Dark on light. If you put light on dark the dark shows through. Dark on light is better.

I have white on white but it’s not a smooth transition.

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If you're talking fabric cover, I would not expect any overlap except on the leading/trailing edges, wing tips, and the 4 corners of the fuselage. Usually, these are then covered with pinked tape (or ripped tape in the case of WWI models). Any color transitions are usually paint on paint, not covering on covering. I also don't cover the ends of the ailerons or the wing cut-out for the ailerons because of all the overlaps. I brush on thinned epoxy (preferably laminating epoxy), wait a few minutes and wipe off. After it dries, a light sand with 320 and its ready for primer/paint.

The edges are where the overlaps are. I set it aside for a little bit while I recover another airplane. Maybe it won’t look quite as bad when I pick it back up and I will try to very lightly sand the seams. What kind of pinking tape do you use and where can I get it at? It’s on a 1/4 scale Space Walker. I am not trying to get exactly scale I just would like it presentable.

Don't try to sand the seams on a fabric-covered plane without a layer of paint over them. You'll make a frayed mess that no amount of paint will hide. Once you've layed down some paint, you can wet sand the seams being careful not to cut into the fabric. Several rounds of paint/wet sand will help smooth out and minimize the seams.

There are 2 types of pinking tape that I've used; Pink-It (dbalsa.com) makes iron-on tapes from Solartex and F&M Enterprises (Stits.com) makes tapes non-adhesive tapes that are put down with their Poly-Tone paint products. I've used both and each has its pros and cons. Either will work if you're using something like dope or poly tone paints. If you're using automotive or latex paints, I'd use the Pink It tapes. There is also a UK source of pinking tape but I can't remember the site and non-scale pinking tape that you can get at the drug store. You might get some ideas from the following article: https://www.modelairplanenews.com/ho...and-rib-tapes/