aileftech/hex-colors.txt

here is an all awk version, slightly more readable than the sed version

awk '{$0=toupper($0)} /^[A-FOI]{6,6}$/{gsub("I",1); gsub("O",0); print "#" $0}' file

Pretty gosh darn happy with this now c:

Not pure bash, I think that the coreutils's conciseness (tr, fold, xargs) is indispensable and grep is just so much faster (something does feel a little slow, donno if it's the sub-shells, or the arrays, haven't put my finger on it). I think it's concise, and clear... so long as one knows <<<, <(), IFS, and overlooks the entire BG_RGB pipeline (for which one ought to know a relatively obscure feature of printf, xargs, and (new to me) fold). Gotta love shell.

while read -r WORD; do
  while read -r HEX; do
    IFS=" "
    read -r -a BG_RGB <<< "$(fold -w2 <<< $HEX | xargs -I {} printf '%d ' 0x{})"
    read -r -a FG_RGB <<< "$(for component in ${BG_RGB[*]}; do printf '%d ' $((255 - $component)); done)"
    IFS=";"
    printf '\033[48;2;'"${BG_RGB[*]}"'m\033[38;2;'"${FG_RGB[*]}"'m '"$HEX"' \033[0m %s\n'
  done < <(tr 'IOS' '105' <<< ${WORD^^})
done < <(grep -Pi "^[A-FIOS]{6,6}$" /usr/share/dict/words)
# time for a in {1..10}; do ... ; done
# real  0m7.699s
# user  0m8.047s
# sys   0m1.301s

Edit:

something does feel a little slow

It was xargs, 'bout 50% faster without it (specifically not because of any other change I made to refactor it out, though most tweaks do push it over real 0m4s).

while read -r WORD; do
  while read -r HEX; do
    IFS=$'\n'
    BG_RGB=( $(fold -w2 <<< $HEX | while read -r COMP; do printf '%d\n' 0x$COMP; done) )
    FG_RGB=( $(for COMP in ${BG_RGB[*]}; do printf '%d\n' $((255 - $COMP)); done) )
    IFS=";"
    printf '\033[48;2;'"${BG_RGB[*]}"'m\033[38;2;'"${FG_RGB[*]}"'m '"$HEX"' \033[0m %s\n'
  done < <(tr 'IOS' '105' <<< ${WORD^^})
done < <(grep -Pi "^[A-FIOS]{6,6}$" /usr/share/dict/words)
# time for a in {1..10}; do ... ; done
# real  0m3.908s
# user  0m3.711s
# sys   0m0.716s

Edit: sed is slightly faster than grep or awk (for matching words, on my machine), and dropping the nested while loop into what is now sed's pipeline saves a ton of time. This is as fast as I think it gets, at least without using awk or sed for more than just what grep can do.

while read -r HEX; do
  IFS=$'\n'
  BG_RGB=( $(fold -w2 <<< $HEX | while read -r COMP; do printf '%d\n' 0x$COMP; done) )
  FG_RGB=( $(for COMP in ${BG_RGB[*]}; do printf '%d\n' $((255 - $COMP)); done) )
  IFS=";"
  printf '\033[48;2;'"${BG_RGB[*]}"'m\033[38;2;'"${FG_RGB[*]}"'m '"$HEX"' \033[0m %s\n'
done < <(sed -n 's/^[A-FIOSa-fios]\{6\}$/\U&/p' /usr/share/dict/words | tr 'IOS' '105') \
# time for a in {1..10}; do ... ; done
# real	0m2.318s
# user	0m2.227s
# sys	0m0.464s

Edit: I gotta go to bed :c
But just as a quick and dirty point of comparison, has an (extra) advantage bc the loop is unrolled (not that it makes a difference):

#!/usr/bin/env -S awk --non-decimal-data -f
{$0=toupper($0)}
/^[A-FIOS]{6,6}$/ {
  gsub("I",1);
  gsub("O",0);
  gsub("S",5);
  print "\033[48;2;" \
        000+("0x"substr($0,1,2)) ";" \
        000+("0x"substr($0,3,2)) ";" \
        000+("0x"substr($0,5,2)) "m" \
        "\033[38;2;" \
        255-("0x"substr($0,1,2)) ";" \
        255-("0x"substr($0,3,2)) ";" \
        255-("0x"substr($0,5,2)) "m" \
        " #" $0 \
        " \033[0m"; }
# time for a in {1..10}; do ... ; done
# real	0m0.539s
# user	0m0.532s
# sys	0m0.008s

Where is #BADA55 (or this is clean version)?

@dainiuxt it's on the "enable" list that my script uses

https://gist.github.com/aileftech/dd4f5598b1f3837651fdf16e5abc3ffb?permalink_comment_id=4321772#gistcomment-4321772

What if you take into account hex codes with 3 characters?

@lucasqueiroz

#AAA
#ABC
#ABE
#ACE
#ADA
#ADD
#AD0
#A1D
#A55
#BAD
#BBC
#BED
#BEE
#B1B
#B1D
#B0A
#B0B
#B00
#B5C
#CAB
#CAD
#CB1
#C1D
#C0B
#C0D
#C00
#C05
#DAB
#DAD
#DEB
#DFC
#D1D
#D1E
#D0C
#D0E
#D5C
#EBB
#E5C
#E5E
#FAD
#FED
#FEE
#F1B
#F0B
#F0E
#1B1
#1CE
#1DA
#111
#0AF
#0DD
#0DE
#0ED
#0FF
#5AD
#5EA
#5EC
#5EE
#51C
#50B
#50D
#55E