# set terminal pngcairo  transparent enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'histogram_colors.1.png'
unset border
set boxwidth 0.8 absolute
set style fill   solid 1.00 border rgb "black" 
set key title "  Category  " center
set key lmargin top vertical Right noreverse enhanced autotitle nobox
set key invert samplen 4 spacing 1 width 2 height 0
set key maxcolumns 1 maxrows 0 offset character 2, 0
set style histogram columnstacked title textcolor lt -1
set style data histograms
set xtics border in scale 1,0.5 nomirror norotate  autojustify
set xtics  norangelimit 
set xtics   ()
unset ytics
set cbtics border in scale 1,0.5 nomirror norotate  autojustify
set title "Column-stacked histogram colored by data category" 
set xrange [ * : * ] noreverse writeback
set x2range [ * : * ] noreverse writeback
set yrange [ * : * ] noreverse writeback
set y2range [ * : * ] noreverse writeback
set zrange [ * : * ] noreverse writeback
set cbrange [ * : * ] noreverse writeback
set rrange [ * : * ] noreverse writeback
set colorbox vertical origin screen 0.9, 0.2 size screen 0.05, 0.6 front  noinvert bdefault
color(category) = 100 + strstrt(alphabet, category)
NO_ANIMATION = 1
alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
## Last datafile plotted: "$Set3"
plot for [data in "$Set1 $Set2 $Set3"]      data using 2:(color(strcol(1))) lc variable title data,      for [i=1:12] keyentry with boxes lc color(alphabet[i:i]) title alphabet[i:i]