title: Mapping between data and line color in gnuplot
body: <p>I want to create a simple histogram in gnuplot and want to adapt the color of the bars according to the data. Currently, I am struggling with the mapping between color and data.
  Let's say I have the following data file:</p>
  
  <pre><code>X, 500.00, 100.00, 1
  Y, 600.00, 200.00, 2
  </code></pre>
  
  <p>I generate the histogram with the following code:</p>
  
  <pre><code>reset
  fontsize = 12
  set terminal png
  set output "file.png"
  set style fill solid 1.00 border 0
  set style histogram errorbars gap 2 lw 1
  set style data histogram
  set xtics rotate by -45
  set grid ytics
  set xlabel "label"
  set ylabel "label"
  set yrange [0:*]
  set datafile separator ","
  plot 'data.dat' using 2:3:4:xtic(1) ti "" lc variable
  </code></pre>
  
  <p>Now I want to create a mapping between the fourth column in the data and the color, e.g. 1 -> yellow, 2 -> blue.
  I assumed that I can define something like the following</p>
  
  <pre><code>set style line 1 linecolor rgb "yellow"
  set style line 2 linecolor rgb "blue"
  </code></pre>
  
  <p>but this code is not working since it defines styles and not colors. On the other hand I have read in the documentation that "rgb variable" is only available in 3D plotting mode (splot), so I think in this terms my whole approach might go in a wrong direction. </p>
  
  <p>Does anyone know how to realise the mapping between data and line colors?</p>