Surfer allows you to create a save custom colormaps (CLR) and levels files (LVL) in the user interface as described on the Colormap Editor help page.  If you'd prefer to create a custom LVL file via automation, the script below will prompt the user for a name and location as well as the desired contour levels.

To run this script:

1. Copy the script below, or download the attached BAS file: rainbow.bas.
2. In a Windows Explorer window, navigate to C:\Program Files\Golden Software\Surfer.
3. Double click on Scripter.exe to launch Scripter.
4. Press Ctrl+A to select all of the existing lines then press Delete.
5. If you copied this script, press Ctrl+V to paste it into Scripter. If you downloaded it, click File | Open, select the BAS file from your downloads directory, and click Open.
6. Click Script | Run to run the script.
    

*********

'============================================================================
'	RAINBOW.BAS
'
'	This script creates a LVL file with colors ranging from 
'		red-yellow-green-cyan-blue.
'    
'	Contour lines are solid by default.  For invisible contour lines, change
'		Solid to Invisible in s1$.
'============================================================================

Sub Main
Dim contour(1000)
header$ = "'Level Flags LColor LStyle LWidth FFGColor FBGColor FPattern FMode"
q$ = Chr$(34)  ' a double quote
sp$ = Space$(1) ' a space
s1$ = "0 " + q$ + "Black" + q$ + sp$ + q$ + "Solid" + q$ + " 0 " + q$
s3$ = q$ + sp$ + q$ + "White" + q$ + sp$ + q$ + "Solid" + q$ + " 2"
form$ = s1$ + s2$ + s3$
lvlfile$=InputBox$( "Name of level file to create. Must include full file path and .lvl extension. For example: c:\temp\test.lvl")
cmin=Val(InputBox$( "Minimum contour value: "))
cmax=Val(InputBox$( "Maximum contour value: "))
interval=Val(InputBox$( "Contour interval: "))
Open lvlfile$ For Output As #1
nlvls = (cmax - cmin) / interval - 1      ' was + 1, not -1
For i = 1 To nlvls
	contour(i) = cmin + i * interval      ' was (i - 1) *, not i *
Next 
end2 = Int(nlvls / 2)
end1 = Int(end2 / 2)
end3 = end2 + Int((nlvls - end2) / 2)
Print #1, "LVL2"
Print #1, header$
For i = 1 To end1
	r = 0
	b = 255
	g = Int((255 / (end1 - 1)) * (i - 1))
	red$ = LTrim$(Str$(r))
	green$ = LTrim$(Str$(g))
	blue$ = LTrim$(Str$(b))
	Debug.Print contour(i);" ";red$;" "; green$;" "; blue$
	Print #1, contour(i);" ";s1$+"R"+red$+" G"+green$+" B"+blue$+s3$
Next 
For i = end1 + 1 To end2
	r = 0
	g = 255
	b = 255 - Int(255 / (end2 - end1) * (i - end1))
	red$ = LTrim$(Str$(r))
	green$ = LTrim$(Str$(g))
	blue$ = LTrim$(Str$(b))
	Debug.Print contour(i);" ";red$;" "; green$;" "; blue$
	Print #1, contour(i);" ";s1$+"R"+red$+" G"+green$+" B"+blue$+s3$
Next 
For i = end2 + 1 To end3
	b = 0
	g = 255
	r = Int(255 / (end3 - end2) * (i - end2))
	red$ = LTrim$(Str$(r))
	green$ = LTrim$(Str$(g))
	blue$ = LTrim$(Str$(b))
	Debug.Print contour(i);" ";red$;" "; green$;" "; blue$
	Print #1, contour(i);" ";s1$+"R"+red$+" G"+green$+" B"+blue$+s3$
Next 
For i = end3 + 1 To nlvls
	r = 255
	b = 0
	g = 255 - Int(255 / (nlvls - end3) * (i - end3))
	red$ = LTrim$(Str$(r))
	green$ = LTrim$(Str$(g))
	blue$ = LTrim$(Str$(b))
	Debug.Print contour(i);" ";red$;" "; green$;" "; blue$
	Print #1, contour(i);" ";s1$+"R"+red$+" G"+green$+" B"+blue$+s3$
Next 
Close #1
'LVL2
' 52200 0 "Black" "Invisible" 0 "R0 G60 B255" "White" "Solid" 2
	
End Sub

Updated October 2021