Color listing in xterm terminal - linux

Question

I installed a minimal debian and i'm trying to set everything by myself, so i'm trying to tune my default terminal Xterm by giving it some colors, after some research i found that this can be done either by editing the .Xresources file so i can give the first 16 colors in Hexa code (#numbers) or by editing the .bashrc file.
After some research seems like the second solution is more dynamic 'cause i can specify the colors of files by extensions, the problem is that all the articles on the net use a color code very weird :
.gz 01;31
.bz2 01;31
.deb 07;31
.rpm 01;31
.jar 01;31
I want to know if there's a way to use RGB code color or hexa color so i can have more flexibility with my directory and files listings.

Answer 1

AFAIK, there is no RGB support, terminal emulators are limited to display a limited set of colors (a palette with 64 combinations of foreground and background, if I'm not mistaken). If ease of use is what concerns you, you can always declare several variables for the predefined colors, something like:
readonly BLACK_FONT_BLACK_BACKGROUND='30;40'
readonly BLACK_FONT_RED_BACKGROUND='30;41'
readonly BLACK_FONT_GREEN_BACKGROUND='30;42'
readonly BLACK_FONT_YELLOW_BACKGROUND='30;43'
...
readonly WHITE_FONT_CYAN_BACKGROUND='37;46'
readonly WHITE_FONT_WHITE_BACKGROUND='37;47'
And use them later like:
.gz $BLACK_FONT_YELLOW_BACKGROUND
The following is a table with the color codes for foreground and background:
Color Foreground Background
-------------------------------
black 30 40
red 31 41
green 32 42
yellow 33 43
blue 34 44
magenta 35 45
cyan 36 46
white 37 47
-------------------------------
If generating all the color names variables manually is too tedious, you can use the following python script:
colors = ['black', 'red', 'green', 'yellow', 'blue', 'magenta', 'cyan', 'white'];
index = 0
for x in ["{0}_FONT_{1}_BACKGROUND='{2};{3}'".format(colors[i].upper(), colors[j].upper(), i + 30, j + 40) for i in xrange(0, 8) for j in xrange(0, 8)]:
print x.ljust(38) + "#" + str(index)
index += 1

Answer 2

I'm sorry, but you can't use the RBG color code (or HSV, or HCL). You may find the documentation with:
$ man 5 dir_colors

Answer 3

As noted by #Leonardo Fontenelle, the place to start reading about GNU ls coloring is the dir_colors manual page. The numbers used, such as 01;31 are the constants associated with what the manual page refers to as "ISO 6429 (ANSI) color sequences". Actually the manual page is a little more obscure than it ought to be:
the constants are parameters used in the ISO 6429 SGR (set graphic rendition) control sequence. The actual standard is very detailed (see ECMA-48).
01 happens to be the standard code for bold (the manual refers to it using the Linux-centric "brighter colors*).
as noted by #higuaro, codes 30-37 and 40-47 form a color palette; all of the colors shown on the terminal at any moment come from the current palette.
there is more than one way to update the color palette used by xterm; none of those are directly related to the ls configuration because the numbers used for referring to the palette do not contain the color information by themselves.
you can display the colors and video attributes using the ncurses tput utility, e.g., tput setaf 7.
some (relatively) recent ls configurations use additional color codes outside the 30-37 / 40-47 palette, e.g., for the aixterm 16-color feature, or the xterm 88-colors or 256-colors. The dir_colors manual page does not mention this.