pub const ANSI_256: [Rgb; 256];Expand description
The 256 colors an xterm-compatible terminal addresses by index, so that
entry i is what the terminal paints for 38;5;i.
Three regions, and they are not equally trustworthy. 0-15 are the ANSI_16
system colors, which every emulator lets the user repaint. 16-231 are a
6x6x6 RGB cube and 232-255 a 24-step gray ramp, and those 240 are fixed.
So a color whose whole job is to be told apart from another should quantize
against ANSI_240 rather than against this table: a match landing in the
low sixteen is a match against a color the user may have moved.