Sphere + Sundry only uses botanically derived dyes/ coloring agents, which aren't as fixed or shelf-stable as most commercial/ artificial dyes. They will change over time, especially with improper storage (primarily exposure to light).
Changes in color do not change magical efficacy for the vast majority of offerings. It's just part of the charm of how natural materials age, and part of why the general recommendation is to use talismanic materia within a year of acquisition (though many Forms truly last much longer!).
When WATERS or KOLONIAS change color or start looking different, it is often the result of colloidal gold, silver, or copper chemically interacting with essential oils, chlorophyl, and/ or natural dying agents. Shaking vigorously can sometimes reinstate the original look, depending on the cause.