The varnish also protects the rod from damage so choosing an exterior grade spar type varnish is essential. One of the big cosmetic differences with modern urethane spars is they don't impart colour like the old spar formulations. The amber and honey tones of the varnish added character to the older rods. Many modern finishes are so clear they appear antiseptic and many rods look too "clean" to my eye. Builders can add colour by flame toning or ammonia toning the rod. Using some scrap bamboo try adding some colour to your rods and test them with your varnish. You may like the results.
Like all aspects of rodbuilding it is a personal choice but study other rods and see if you can add a little colour in to your life.