: Does anyone have any recommendations for a good clear finish that
: does not yellow?

All the finishes I know of tend to yellow slightly, if you give them enough time. The thicker you apply a finish the more it will yellow with time.

Here is the physics behind it: Ultraviolet light rays are very destructive and will cause many finishes and plastics to decompose over time. As it does so, it oxidizes, (like burning or rusting) and the result is a light brown color. it is so light that it looks yellow. But it is burnt plastic. So the manufacturers put in materials which either block, or absorb, the UV. These materials appear yellow, because they are absorbing their complementary colors: the violet and ultra violet wavelengths of light.

With many coats of a material the thickness will grow, and the many layers of filters will become more visible. it is very gradual. Just like a pool of water looks blue, but a glass of water is clear.

Conventional varnishes tend to give the "warmest" finish. In this case, "warm" means it is yellow. Interior urethane finishes have no protection from UV, and you might find one which was "water clear", but I haven't heard anything good about using interior urethanes on kayak skins, and I have read of one bad result where the urethane just peeled off. So, while it is clear, it is not a good idea. The exterior urethanes would be the next in line for clarity and lack of color--but they would still be a bit yellow, and get more yellow as they aged.

If you want things to be a nice bright white, use paint. Or, do like the laundry detergent people advertise: add a whitening and brightening agent to your varnish. I'm not sure where you would find something which would be compatible with your urethane finish, but there are clear materials which reflect a lot of blue light, and which would balance out the yellow light reflected by the blue absorbing materials mixed in by the manufacturer.
Laundry "bluing" used to be used for this. You might see if you can find some at the local grocery store in the laundry soap area. I really don't know if it would work, though.

Good luck in your search.

PGJ