Using varnish, there is only one way to find out what the final result will look like. Do test wraps. The final color depends not only on the thread type or color but also the blank color (flamed, blonde, etc) when the wraps go translucent the blank shows through to some extent. It seems to me that the darker the original thread color, the greater the darkening effect of the varnish. At least with silk.
CP brings its own set of problems. You must make sure that every bit of thread is saturated with CP or the wrap will go blotchy when the varnish hits the spots that didn't get enough. Common problems are not getting the CP into the gap beside the guide foot or not letting it flow over the edge onto the blank slightly. It may take as many as three coats of CP to seal everything up.
Just try everything before committing to the final selection.
Shaky;
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