I am rewrapping a ferrule on a bamboo rod and the wraps looked like yellow and black classic twist till I got them off, then they turned out to be white/black, with a yellow varnish on them. Is there any varnish that has a yellow shade to it?

The non-water based varnishes all turn yellow after a bit. Just give it a few months, or weeks.

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That leaves me to wonder if the original builder intended the wraps to appear white and black... or yellow and black.

If the former is true you might want to redo all the wraps with a water based varnish.

Almost oil based varnishes have some ambering properties right from the beginning. The only exception is soya based varnishes, and that's just temporary since the alkyd resin they are made with will yellow pretty quickly. So classic rod makers only had varnishes that they knew would be amber colored right from the start, or would turn yellow quickly. (I'm not at all sure that soya varnish was around before mid-century.) We can be sure they didn't use varnishes that were water clear. I doubt they would have used bleached shellac.

Almost oil based varnishes have some ambering properties right from the beginning. The only exception is soya based varnishes, and that's just temporary since the alkyd resin they are made with will yellow pretty quickly. So classic rod makers only had varnishes that they knew would be amber colored right from the start, or would turn yellow quickly. (I'm not at all sure that soya varnish was around before mid-century.) We can be sure they didn't use varnishes that were water clear. I doubt they would have used bleached shellac.

Almost oil based varnishes have some ambering properties right from the beginning. The only exception is soya based varnishes, and that's just temporary since the alkyd resin they are made with will yellow pretty quickly. So classic rod makers only had varnishes that they knew would be amber colored right from the start, or would turn yellow quickly. (I'm not at all sure that soya varnish was around before mid-century.) We can be sure they didn't use varnishes that were water clear. I doubt they would have used bleached shellac.

What you are seeing is very common in older bamboo rods. I'll bet that the original company used shellac or lacquer as a CP then varnished over it. A very common technique. At the time that rod was originally varnished the varnish did not have a UV inhibitor which is what causes the yellowing. to recreate that yellow tone takes a lot of work and experimenting with tinting the varnish.
what kind of rod is it? make/ model.

Any of the oil based varnishes offered today will yellow, and do so very quickly.

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