93 thinner highlight colors, the biggest single Citadel range and the one built for transitions.
Reading the Layer range
Layer is the largest Citadel range at 93 colors, and that size is the point. Where Base gives you a foundation, Layer gives you the slightly lighter, slightly different tones you build highlights with, which is why you often see two or three Layer colors that look almost the same on the rack. They are meant to be used in sequence, each a small step up in brightness over the last.
The color spread tilts warm: browns and reds together make up nearly a third of the range, with a strong run of greens and a deep bench of greys for edge-highlighting armor and stone. Blues and purples are present but thinner. There is a single white and no true black here, because black and white foundations belong in Base; Layer assumes you have already undercoated.
If you are new to Citadel, the honest advice is not to buy Layer colors one at a time. They make sense as the highlight partners to a Base color you already use, and the range rewards owning a small ladder of related tones rather than scattering across all 93.