Gnuplot change color of bars in histogram

Question

is it possible to change the color of bars in a Gnuplot script dynamically? I have the following script

reset
fontsize = 12
set term postscript enhanced eps         


        

Answer 1

You could split your data file into two parts, positive values and negative, and plot them separately:

plot 'bm_speedup_pos.dat' using 2:xtic(1) ti "Faster" linecolor rgb "#00FF00", \
     'bm_speedup_neg.dat' using 2:xtic(1) ti "Slower" linecolor rgb "#FF0000"

Or, if you only need to generate a few graphs, a few times, a common technique is to generate the raw graph in gnuplot, then post-process it in an image editor to adjust the colors. If you go that route, I suggest having gnuplot generate the graph in SVG format, which will give you much better looking graphs than any of the bitmap formats.