Set, backup and restore colors in the terminal

Question

I use this program to display all color available in the terminal. That waht I get:

1. This program doesn't show me colors below 100. Why? Is there a way to display them.
2. Is the are way to change the n-th color for some #rrggbb value? Or this colors a predefined?
3. If I can change colors (see question 2) is there a way to export and import this values?

Answer 1

How many colours are supported and how to change the foreground and background colour depends on the terminal.

The terminfo database is usually there to help you come up with the right sequence.

Most colour terminals support the ANSI colour escape sequences to change the foreground and background colours 0 to 7.

That's:

• set foreground colour $n: printf "\33[3${n}m"
• set background colour $n: printf "\33[4${n}m"

Some (rare) terminals (like emu) use different sequences for those ANSI colours.

Some (rare) terminals like the QNX console have different escape sequences and different colours.

Some (rare) work with colour pairs. You define a colour pair for background and foreground, and then have an escape sequence to select the pair you want to use.

Now, xterm and most modern Free Software terminal emulators extend the basic 8 ANSI colours, to up to 16 (where 8 to 15 are brighter versions of the ANSI colours 0 to 7), 88 or 256 colours for some.

Some terminals like rxvt only support 8 colours, but use the brighter colours if bold is also on (for the foreground) or blink (for the background). \033[34;1m will give a brighter blue than \033[34m.

The most portable way to use colours is to use the terminfo database.

It can be via the tput command. tcsh and zsh also have an echoti builtin for that.

Provided the terminfo database is correct and the value of $TERM correctly reflects the terminal you're using:

tput colors

Will give you the number of colours supported by your terminal.

Nowadays, except for the rare exceptions mentionned above, you can assume that your terminal will support ANSI colours. The terminfo capabilities for the ANSI background and foreground colours are setab and setaf. If the terminal supports more than 8 colours, you can still use that capability to query them.

tput setaf 233

If the terminal supports 256 colors should output the correct escape sequence for that colour 233.

For xterm, setaf outputs \033[30m..\033[37m for colours 0 to 7, \033[90m..\033[97m for colours 8 to 15 and \033[38;5;16m..\033[38;5;255m for colours 16 to 255.

\033[38;5;0m..\033[38;5;15m will also work but are 4 bytes longer than their more portable equivalent for colours 0 to 15.

So, to test all the colours supported by the terminal. If it supports ansi colours:

i=0; n=$(tput colors); while [ "$i" -lt "$n" ]; do
  tput setaf "$i"; printf %04d "$i"
  i=$((i + 1))
done

If it supports other colours:

i=0; n=$(tput colors); while [ "$i" -lt "$n" ]; do
  tput setf "$i"; printf %04d "$i"
  i=$((i + 1))
done

If it works with colour pairs (like hpterm-color):

i=0; n=$(tput pairs); while [ "$i" -lt "$n" ]; do
  tput scp "$i"; printf %04d "$i"
  i=$((i + 1))
done

Now, to redefine a colour or colour-pair, that also varies between terminals.

There's a initc terminfo capability to redefine a given colour for those terminals that can do it. And initp to redefine a pair.

For instance to redefine the colour 1 as bright white:

 tput initc 1 1000 1000 1000

With xterm, that sends the sequence: \033]4;1;rgb:FF/FF/FF\033\.

To redefine the colour pair 1 to white on black on terminals that work with pairs:

 tput initp 1 1000 1000 1000 0 0 0

Answer 2

Since you are using gnome-terminal there is no need to change RGB values. Recent gnome-terminal (since v. 3.12) supports true 24 bit colours (16 millions). You can set them with \e[38;2;R;G;B. For example

printf '\e[38;2;100;200;200mTest\e[0m\n'

If you see blue text your terminal supports 24 bit colours.

---

However, if you wanna stick with 256 colours I recommend the following script to display all possibilities, which displays them arranged in blocks to easily pick up the desire one (with less or more of some RGB component):

#!/bin/bash

trap 'echo "Bye"; exit 1' INT

echo "PALETTE OF 8 COLORS"
for i in {30..37}; do printf "\e[1;${i}mTest%-3u \e[0m" "$i"; done; echo
for i in {90..97}; do printf "\e[${i}mTest%-3u \e[0m" "$i"; done; echo
for i in {30..37}; do printf "\e[${i}mTest%-3u \e[0m" "$i"; done; echo
for i in {30..37}; do printf "\e[2;${i}mTest%-3u \e[0m" "$i"; done; echo -e "\n"

echo "PALETTE OF 256 COLORS"
j=8
for i in {0..255}; do
    [[ $i = 16 ]] && j=6
    [[ $i = 232 ]] && j=24
    printf "\e[38;5;${i}mTest%-3u \e[0m" "$i"
    [[ $(( $(( $i - 15 )) % $j )) = 0 ]] && echo
    [[ $(( $(( $i - 15 )) % $(( $j * 6 )) )) = 0 ]] && echo
done
exit 0

Answer 3

As I have found I can get all the colors by

for i in {0..255} ; do printf "\x1b[38;5;${i}mcolour${i}\n"; done

It is possible to change the RGB values in ~/.Xresources like this:

xterm*color4: CornflowerBlue
URxvt*color1  : #ff0000
URxvt*color8  : #888888

but not all terminal emulators respect this values. URXVT does, gnome-terminal doesn't

Answer 4

The program is buggy as it pads the numbers with spaces to 3 characters. E.g. prints "[[48;5; 42m (with space) which doesn't work instead of ^[[48;5;42m (without space) which would work.