Symbol color in postscript terminal - gnuplot

Question

I've a top view of a pm3d plot in black and white. I am rendering the plot via postscript terminal enhanced eps.
I've to place zeta symbol over the data in white color. I've used
set label "{/Symbol=11 \245} = 1.0" at first 0.25, first 0.75 tc rgbcolor "#FFFFFF"
command. But the symbol is being rendered in black color. My terminal command is
set term postscript eps enhanced color font "Helvectica, 9" size 6.5cm, 6cm.
I've removed the tag color, and yet the color is still black.
What could be the command for a white symbol? I'm using gnuplot version 5.2.
My *.eps output:
/Helvetica findfont 90 scalefont setfont
1.000 UL
LTb
LCb setrgbcolor
1105 1598 M
63 0 V
1.000 UP
stroke
LCb setrgbcolor
644 1547 M
[ [(Symbol) 110.0 0.0 true true 0 (z)]
[(Helvetica) 90.0 0.0 true true 0 ( = 1.0)]
] -36.7 MLshow
I've attached below the image of the output, where I've shown what label appears as (I've moved it to x position 0.5).

Answer 1

Your command works correctly when run here, or at any rate it prints a label in white. Note, however
The symbol \245 renders as ∞ rather than ζ. I think you want \172.
The font name Helvetica is misspelled.
To make sure the label is not hidden by the pm3d surface you should add the "front" attribute.
I split the command into three lines for clarity
set label 1 "{/Symbol=11 \172} = 1.0" at first 0.25, first 0.75
set label 1 tc rgbcolor "#FFFFFF"
set label 1 front
The corresponding code in the *.eps output looks like this:
1.00 1.00 1.00 C
1144 2527 M
[ /Symbol reencodeISO15 def
[(Symbol) 110.0 0.0 true true 0 (z)]
[(Helvetica) 90.0 0.0 true true 0 ( = 1.0)]
] -36.7 MLshow
The first line sets the color to white.
The second line moves to the position on the page.
The following four lines print the label.
Does your output produce a different sequence of PostScript commands? Showing the relevant fragment of the output might help debug the problem.
EDIT
The equivalent section of *.eps output if the terminal is set term postscript eps mono rather than set term postscript eps color:
LCb setrgbcolor
1144 2527 M
[ /Symbol reencodeISO def
[(Symbol) 110.0 0.0 true true 0 (z)]
[(Helvetica) 90.0 0.0 true true 0 ( = 1.0)]
] -36.7 MLshow