Fill up rainbow spectrum under histogram.

 

unset label
unset key
unset label
set terminal wxt font ' ,25'

set datafile separator ','
csv_input = "Histogram_of_Phase.csv" #input file name

stats csv_input every ::1 u 2:3 nooutput
lmax = STATS_max_y #maximum of the siganl
lmin = STATS_min_y

set xrange [0:180]
unset ytics
set xtics 0,60,180

set pm3d map
set palette defined (0 "black", 30 "blue", 73 "green", 143 "red", 180 "grey")

set palette color
set key autotitle columnhead
splot [0:180][0:1] x

set samples 1000
set style fill solid
plot csv_input u 2:3:2 w boxes palette title "",\
csv_input u 2:3 w line lc "black" lw 5 smooth csplines title ""

#plot csv_input u 2:3:2 w boxes palette

unset colorbox