title: How to highlight regions of plot with gnuplot
body: <p>I'd appreciate if somebody can help with this question. 
  I am working with a radar (or spiderweb) plot with gnuplot 5.0.0:</p>
  
  <p><img src="https://i.stack.imgur.com/wC9B1.jpg" alt="enter image description here"></p>
  
  <p>The scale and range in all axes is the same. The numbers at and beyond 1 have a special meaning and I would like to highlight that. </p>
  
  <p>I am thinking of three things that would increase visibility:</p>
  
  <ol>
  <li><p>Simply make the tick mark at 1 (labelled "Limit") boldfaced. How could I highlight just a specific tick and label? </p></li>
  <li><p>I could also highlight the circular dashed line at level 1</p></li>
  <li><p>On the plot itself I'd like to have the background colored differently for radius > 1. </p></li>
  </ol>
  
  <p>How can I achieve either of the three options above?  All three would be ideal of course, but just a a minimum differentiation from the rest of that value would help.</p>
  
  <h2>This is what generated the plot in the link:</h2>
  
  <pre><code>set term x11
  set title "My title "
  set polar
  set angles degrees
  npoints = 6
  
  a1 = 360/npoints*1
  a2 = 360/npoints*2
  a3 = 360/npoints*3
  a4 = 360/npoints*4
  a5 = 360/npoints*5
  a6 = 360/npoints*6
  
  set grid polar 360
  set size square
  set style data lines
  
  unset border
  
  set grid ls 0
  set linetype 1 lc rgb 'red' lw 2 pt 7 ps 2
  
  M=2.2
  set arrow from 0,0 to first M*cos(a1), M*sin(a1)
  set arrow from 0,0 to first M*cos(a2), M*sin(a2)
  set arrow from 0,0 to first M*cos(a3), M*sin(a3)
  set arrow from 0,0 to first M*cos(a4), M*sin(a4)
  set arrow from 0,0 to first M*cos(a5), M*sin(a5)
  set arrow from 0,0 to first M*cos(a6), M*sin(a6)
  
  a1_min = 0
  a1_max = 1
  a2_min = 0
  a2_max = 1
  a3_min = 0
  a3_max = 1
  a4_min = 0
  a4_max = 1
  a5_min = 0
  a5_max = 1
  a6_min = 0
  a6_max = 1
  
  set label "M1" at M*cos(a1),M*sin(a1) center offset char 1,1
  set label "M2" at M*cos(a2),M*sin(a2) center offset char 1,1
  set label "M3" at M*cos(a3),M*sin(a3) center offset char 1,1
  set label "M4" at M*cos(a4),M*sin(a4) center offset char 1,1
  set label "M5" at M*cos(a5),M*sin(a5) center offset char 1,1
  set label "M6" at M*cos(a6),M*sin(a6) center offset char 1,1
  
  
  set xrange [0:1]
  set yrange [0:1]
  
  set xtics axis 0,0.5,M
  unset ytics
  
  set rrange [0:M]
  
  set rtics (""0,""0.25,""0.5,""0.75,"Limit"1,""1.25,""1.50,""1.75,""2)
  set rtics scale 0 format ''
  
  set style fill transparent solid 0.5
  set style function filledcurves y1=0.5
  set grid noxtics nomxtics noytics nomytics front
  
  
  plot  '-' u ($1==1?a1:($1==2?a2:($1==3?a3:($1==4?a4:($1==5?a5:($1==6?a6:$1)))))):($1==1?(($2-a1_min)/(a1_max-a1_min)):($1==2?(($2-a2_min)/(a2_max-a2_min)):($1==3?(($2-a3_min)/(a3_max-a3_min)):($1==4?(($2-a4_min)/(a4_max-a4_min)):($1==5?(($2-a5_min)/(a5_max-a5_min)):($1==6?(($2-a6_min)/(a6_max-a6_min)):$1)))))) w filledcurve lt 1 title "AAA",\
   '-' u ($1==1?a1:($1==2?a2:($1==3?a3:($1==4?a4:($1==5?a5:($1==6?a6:$1)))))):($1==1?(($2-a1_min)/(a1_max-a1_min)):($1==2?(($2-a2_min)/(a2_max-a2_min)):($1==3?(($2-a3_min)/(a3_max-a3_min)):($1==4?(($2-a4_min)/(a4_max-a4_min)):($1==5?(($2-a5_min)/(a5_max-a5_min)):($1==6?(($2-a6_min)/(a6_max-a6_min)):$1)))))) w filledcurve lt 2 title "BBB"
  
  1 2.1
  2 1
  3 0.1
  4 0.5
  5 0.5
  6 0.1
  1 2.1
  EOF
  1 2.2
  2 0.9
  3 0.9
  4 0.2
  5 0.3
  6 0.1
  1 2.2
  EOF
  set output
  </code></pre>