Topside paints, like gelcoat materials, are designed to protect and to look good. Similarly, they have a tendency to fade or change color tone over time.
One-part air-dry paints, such as Interlux Brightside, TotalBoat Wet Edge, Pettit EZ-Poxy, and Epifanes Monourethane are all easy-to-use products that are have only one component. These paints are more affordable, which in the end is a slight compromise on longevity and durability. Over time, these paints will change color, or lose depth, beginning when they are first applied. Bright whites will lose the brightness and fade to an off-white or cream, bold colors will not be as rich, and dark colors will start to lighten. Exposure to UV, salt spray, and wear and tear all increase the rate of fading as well. Once a glossy surface loses its shine, the degradation rate of the color and finish will only increase until the coating fails.
Two-component paints commonly have a base and an activator or curing agent that is mixed in at a specific ratio. These systems have cross-linking chemistry that adds to the durability and robustness of the coating. The more robust resin system protects the color longer, and offers more wear-and-tear durability, which protects the color for a longer period. These paint systems still suffer the inevitable characteristics of color fading.
It should be expected that even a month in the sun or other exposure could make color matching difficult, or seemingly impossible. If a customer applies a coat of paint one year and goes to touch up a spot a year or two later, it should be expected that it will not look the same, even if it came from the exact same can of paint.