WHAT THE 500 IN BLUE-500 MEANS

Summary from the TLDR Design newsletter

Numbers in color scales such as blue-500 may look standardized, but different design systems use them to represent entirely different concepts, including position in a ramp, guaranteed contrast relationships, measured lightness, or semantic roles. Material Design's original 50–900 scale primarily described positions and established 500 as a typical primary color, while systems such as Carbon, Material 3, and Radix give their numbers more explicit meaning. Understanding what a scale actually encodes is important because two colors carrying the same numerical label can have very different lightness, contrast, and intended uses.