I have used ProSeal on several rebuilds and on one new build. I did not find any discoloration. While wet it does seem to darken the color of the thread. I find that the U40 seal has a lot of foam and is more difficult to use. After mixing, I find ProSeal to be even, no bubbles, no form. It goes on easily - be sure to use small amounts and don't leave excess. I have not epoxied my new build but on the rebuilds, I find no change of color or shade. If the product protects from fading, as advertised, then it is an excellent, easy to use product. Water base for easy cleaning of the brush. I recommend ProSeal for color preservation