Terminal Colors – Why Colors Don’t Show in All Terminals

0.5a - Cyan Tumbleweed Plains

The earlier implementations provided with the question rely on a sequence of commands which uses tr and a set of single byte characters. As was explained in this Q&A, the utility cannot process multibyte characters such as Unicode. But leveraging those characters was quite essential in achieving the desired effect. A "solution" was provided which allows to mix the single byte and multi byte chars in a single stream for rendering. The solution developed there is presented and customized here:

Z1=$(echo -en '\xe2\x97\x98') #◘ 1
Z2=$(echo -en '\xe2\x95\x9a') #╚ 2
Z3=$(echo -en '\xe2\x95\x9c') #╜ 3
Z4=$(echo -en '\xe2\x95\x9d') #╝ 4
Z5=$(echo -en '\xe2\x95\x9e') #╞ 5
Z6=$(echo -en '\xe2\x95\x9f') #╟ 6
Z7=$(echo -en '\xe2\x96\x91') #░ 7
Z8=$(echo -en '\xe2\x96\x92') #▒ 8
Z9=$(echo -en '\xe2\x96\x93') #▓ 9
N1=$(echo -en '\xe2\x94\x80') #─ a
N2=$(echo -en '\xe2\x95\x92') #╒ b
N3=$(echo -en '\xe2\x95\x97') #╗ c
N4=$(echo -en '\xe2\x96\xb6') #▶d
N5=$(echo -en '\xe2\x94\xbc') #┼ e
N6=$(echo -en '\xe2\x94\xa4') #┤ f
N7=$(echo -en '\xe2\x95\xa1') #╡ g
Z11="$(tr -dc '123456789a' < /dev/urandom | head -c 1)" //Z11 to Z13 not
Z12="$(tr -dc '123456789a' < /dev/urandom | head -c 1)" // used here (see
Z13="$(tr -dc '123456789a' < /dev/urandom | head -c 1)" //link)

echo -en $(tr -dcs ' ;",15bdef' ' ' < /dev/urandom | head -c $(echo -en "$[$(tput cols) * $(tput lines)]") | sed -e "s/1/$(echo -en "\033[0;36m$Z1\033[0m")/g" -e "s/5/$(echo -en "\033[0;32m$Z5\033[0m")/g" -e "s/b/$(echo -en "\033[1;36m$N2\033[0m")/g" -e "s/d/$(echo -en "\033[1;36m$N4\033[0m")/g" -e "s/e/$(echo -en "\033[0;32m$N5\033[1;32m")/g" -e "s/f/$(echo -en "\033[0;36m$N7\033[1;32m")/g"); tput cup 1
                 ^set^+^chars^ to implement from pool - here 1,5,b,d,e,f... so_________________________^add the appropriate sed subprocessing units for implemented chars i.e. first one we replace "1" with the value of $Z1 and apply color at the same time, then all the chars move down the pipe to all required blocks - we selected to implement 6 chars here so we have 6 sed blocks. 

[N.B. To remove the blank space from the pattern, remove it from both sets: tr -dcs ';",15bdef' '']

PS1="\[\033[1;36m\] $(echo -en '\xe2\x96\x91')$(echo -en '\xe2\x96\x92')$(echo -en '\xe2\x96\x93')[\t]$(echo -en '\xe2\x96\x93')$(echo -en '\xe2\x96\x92')$(echo -en '\xe2\x96\x91') \[\033[7;36m\]$(echo -en '\xe2\x97\x98')$(echo -en '\xe2\x94\xbc')$(echo -en '\xe2\x94\x80')\W$(echo -en '\xe2\x94\x80')\[\033[0;36m\]$(echo -en '\xe2\x94\x80')$(echo -en '\xe2\x94\x80')$(echo -en '\xe2\x94\x80')@$(echo -en '\xe2\x96\xb6')\[\033[0;36m\]"

PROMPT_COMMAND="echo -en '\033[0;36m$(tr -dc '=' < /dev/urandom | head -c $(tput cols))\n\033[01;46m$(tr -dc '~' < /dev/urandom | head -c $(tput cols))\033[0;36m$(tr -dc '=' < /dev/urandom | head -c $(tput cols))'$(tput cuu 2)"

This implementation no longer renders per line but rather prints the whole sequence in one shot at the end of the sed processing. This appears only at login once or generally when bash is launched. Here is one such random pattern at launch (we can see two shades of green and two shades of cyan):

The screens show the result in the standard linux terminal and it works in xterm too. I've used some of those new pattern chars in the PS1 prompt whereas the PROMPT_COMMAND just takes care of the active line and its 2 line padding which use 1 byte chars.

The pattern also matches well my current distribution which calls archbey in .bashrc.:

It's in for Christmas! Cheers people :)

The answer likely has zero to do with GTK or even modern computing, and absolutely everything to do with ANSI/VT100 graphics, which is what the huge majority of terminals emulate. The colors you get are those that are capable of being sent in an eight-bit escape sequence. Yes, theoretically, folks could ramp up the terminal protocol to something New and Improved, but I'm afraid that a) people are pretty happy with the status quo, so there's no real groundswell for any changes, and b) EVERYTHING supports VT100 -- your terminal, that Cisco router over there, the RS-232-accessible BIOS on the server in the server room, my phone... the list goes on. Basically, if it's not connected to an IBM mainframe (in which case 3270 emulation with EBCDIC comes into play -- with pretty much all the same limitations), it's VT100. "Entrenched" barely scratches the surface.

So, until such time as a multi-byte replacement for ANSI/VT100 "graphics" comes into play, I'm afraid we're stuck. I'm aware that the newer terminals do support Unicode characters -- but as far as I'm aware, Unicode addresses just characters, and not colors. There does seem to be some fairly esoteric debate on this (see https://stackoverflow.com/questions/9626115/color-in-the-unicode-standard), but I certainly don't see anything like a firm consensus.

Bottom line: most folk consider it "not broke," so they ain't rushing to fix it.