docs/vt/osc/4.mdx
<VTSequence sequence={["OSC", "4", ";", "Pn", ";", "Pc", "ST"]} />
Query or change the color in the palette at index n depending on the
value of c.
If c is given as the single character ?, then the terminal will respond with
the color specification of the color at index n. If c is a valid
color, then the palette color is changed to it.
Pairs of n and c can be provided multiple times, separated with a
semicolon (;). The terminal may reply with multiple sequences when multiple
queries are made in one request.
[!NOTE] The terminal need not return the color exactly as it was specified.
When a color at a given index is changed, the terminal is allowed to convert the color into its internal representation, then reply in a different format when the same color is queried.
When n is between 0 and 255, the normal 256-color palette is used.
When n is above 255, however, they instead map to
special colors, with 256
mapping to the first special color (bold), 257 the second (underline), etc.
This makes it behave equivalently to OSC 5 with the index
subtracted by 256.