OK so I just finished wrapping a Steffen 7’9” 3/4 wt.
I used size A nylon thread in a rust with a Red burgundy trim. I seen this color combination used here it really popped and looked beautiful.

Not mine!!! The rust got really dark brown and the red turned almost black. I’m using man-of-war varnish no color preserver. In my test area where I saw the results I started rubbing Varnish In the trim thread and letting dry before I used it...Not a whole lot of difference.
I’m looking for a semi translucent effect where you can still see the color of the thread without the rod over powering it.

Right now I have a black glass rod in front of me and I want it Black with blue trim blue or blue with black trim not sure yet but I want a translucent effect where I can still see the blue.

Then I have another MacFarland glass rod that is brown and I’m looking to do the same thing I tried on the other rod so I’m going to use a rust that complements the brown and a burgundy or ruby red trim that pops.

I started thinking I might need to use silk thread to accomplish this so I just ordered a bunch of silk thread in browns,reds & blues.
Along with some real color preserver and some Epoxy finish.

Steer me in the right direction please I’ll figure it out.

Whirlpool,
Thx You are pretty much correct sort of kind of.
I took the rod out into the sunlight....and bam I have Red not dark brown or black.

Thank you again I’ll just have to play around with these next two rods til I get it right.

Clear shellac can be used as the CP to achieve the effect you want. The threads darken slightly but not nearly as much as varnish. It's really a semi-CP. It works under both varnish and epoxy.

It's best to mix fresh from flakes, get the Zinseer spray shellac and spray some into a small plastic measuring cup, the kind used for mixing finishes. This version has been dewaxed so top finishes will stick to it. The stuff in the can may work, but I'm never chanced it. Use 3 coats, but you'll need fewer top coats.