OSC 4 Change Color Palette

The terminal’s palette is the 256 colors that SGR’s color numbers stand for: CSI 31 m uses color 1, CSI 38 ; 5 ; 196 m color 196. OSC 4 ; Pc ; Pt ST changes color Pc to Pt, and OSC 104 ; Pc ST puts it back as it started. These are xterm’s.

• Pt is a color in any form X11’s XParseColor accepts: a name such as red or light sky blue, #rrggbb, or rgb:rr/gg/bb, where each part may have one to four hex digits.
• Pt of ? asks what the color is. The answer is OSC 4 ; Pc ; rgb:rrrr/gggg/bbbb, sixteen bits a part, ended with whichever of ST or BEL ended the question.
• One sequence can carry several pairs, OSC 4 ; 1 ; red ; 2 ; ? ST, mixing changes and questions. xterm stops at the first color it cannot parse or number it does not have, and ignores the rest (ChangeAnsiColorRequest, ReportAnsiColorRequest).
• OSC 104 ST with no number resets the whole palette, and with numbers, OSC 104 ; 1 ; 2 ST, just those (ResetAnsiColorRequest).
• DECSTR and RIS both reset the palette (ReallyReset).

Where the palette starts is the host’s choice, made in xterm with resources such as color1. The cases are run in a terminal given a default xterm’s: black, red3, green3, yellow3, blue2, magenta3, cyan3 and gray90, then their bright versions, for colors 0 to 15 (charproc.c), and the 6×6×6 cube and the gray ramp for 16 to 255 (256colres.h). The answers assume a 24-bit display, where xterm reports each part of a color as its eight bits repeated, cd as cdcd.

xterm also has OSC 5 and OSC 105, which work the same way on its special colors, the ones it can use for bold, underlined, blinking, reversed and italic text. libghostty-vt does keep the palette through DECSTR, but its DECSTR is not implemented at all (see DECSTR).

Validation

OSC4-1: Ask for a color

\e]4;1;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a

OSC4-2: The answer ends as the question did

\e]4;12;?\e\\

|____|
reply \e]4;12;rgb:5c5c/5c5c/ffff\e\\

OSC4-3: From the cube and the gray ramp

\e]4;196;?;244;?\a

|____|
reply \e]4;196;rgb:ffff/0000/0000\a\e]4;244;rgb:8080/8080/8080\a

OSC4-4: Change a color, and text drawn in it

\e[31mA
\e]4;1;#123456\a
\e]4;1;?\a

|A___|
attr 1,1 fg=#123456
reply \e]4;1;rgb:1212/3434/5656\a

OSC4-5: By name, and by rgb:

\e]4;1;light sky blue;2;rgb:f/80/abc\a
\e]4;1;?;2;?\a

|____|
reply \e]4;1;rgb:8787/cece/fafa\a\e]4;2;rgb:ffff/8080/abab\a

OSC4-6: A color it cannot parse stops the rest

\e]4;1;nosuch;2;red\a
\e]4;1;?;2;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a\e]4;2;rgb:0000/cdcd/0000\a

OSC4-7: Reset one color

\e]4;1;red;2;blue\a
\e]104;1\a
\e]4;1;?;2;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a\e]4;2;rgb:0000/0000/ffff\a

OSC4-8: Reset them all

\e]4;1;red;2;blue\a
\e]104\a
\e]4;1;?;2;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a\e]4;2;rgb:0000/cdcd/0000\a

OSC4-9: RIS resets the palette

\e]4;1;red\a
\ec
\e]4;1;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a

OSC4-10: So does DECSTR

\e]4;1;red\a
\e[!p
\e]4;1;?\a

|____|
reply \e]4;1;rgb:cdcd/0000/0000\a