Now here's an interesting thing to mention. Colored slate is never fading. However, it may weather with time due to the oxidation of it's embedded minerals. This causes the color of the tile to change over time, often towards buff, brown, gray or tan tones.

Does slate darken with age?

Unfading Pennsylvania gray slate is soft-gray, longer-lived; Unfading Pennsylvania black slate is rougher, longer-lived; Blue-black "hard-vein" Pennsylvania roofing slates darken with age.

Does slate fade over time?

A Non-Fading Slate is one which changes very little from when it is first quarried and any slight changes will be relatively uniform on the roof. Any slate which is not a Non-Fading slate is known as a Fading slate or Semi Weathering or Weathering Slate. The amount of colour change varies from product to product.