how to fix the problem of the missing color pieces in the colorbox in gnuplot

I met a problem that when I draw a map using gnuplot, there would be a colorbox near the map which looks very weird. I blew up the colorbox and found that there were pieces with missing color, the picture is below. How can I fill the color for the colorbox?

Here are the terminal type and the palette I used in in gnuplot. set terminal postscript portrait color enhanced 12. set palette defined (-6.0 "#1B66B1",
-4.8 "#1B66B1",
-4.8 "#2A85DF",
-3.6 "#2A85DF",
-3.6 "#5FA3E7",
-2.4 "#5FA3E7",
-2.4 "#95C2EF",
-1.2 "#95C2EF",
-1.2 "#C9E0F7",
-0.120000 "#C9E0F7",
0.0 "#FFFFFF",
0.0 "#FFFFFF",
0.120000 "#F6D5CB",
1.2 "#F6D5CB",
1.2 "#EDAB96",
2.4 "#EDAB96",
2.4 "#E48062",
3.6 "#E48062",
3.6 "#DC562E",
4.8 "#DC562E",
4.8 "#AE3F1E",
6.0 "#AE3F1E")

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