# 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  " enhanced   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" 
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]