PDFlib use spot color as text background

I'm trying to use spot color as fill on my text background and I can't seem to make it work

This is my code.

$p->setcolor("fill", "cmyk", 0.0, 1.0, 0.8,0.0);
$red = $p->makespotcolor("Redspot");
$p->setcolor("fill","spot",$red,1.0,0.0,0.0);
$p->fit_textline('spot color back',0,0,"matchbox={boxheight={88% 24.5%} fill={".$red." 1 0 0}} position={center bottom}");

The expected output is a text on top of a box both using Redspot as spot color name and the fill of the box behind it being lighter.

I see a few small problems in your code snippet, but I get it the expected output

when I change your code to:

$fontopt = "fontname=NotoSerif-Regular fontsize=24";

$p->setcolor("fill", "cmyk", 0.0, 1.0, 0.8,0.0);
$red = $p->makespotcolor("Redspot");
$p->setcolor("fill","spot",$red,1.0,0.0,0.0);
$p->fit_textline('spot color back',0,0, $fontopt . 
  " matchbox={boxheight={88% 24.5%} fillcolor={spot ".$red." 0.1}} " .
  " position={center bottom}");

The following have I changed:

• the matchbox option to set the color for the background is fillcolor(see PDFlib 10 API Reference 6.2.1 "Defining Matchboxes")
• for applying a spotcolor in a color option list, you have to add a first keyword spot, then the spotcolor handle (here $red) and then the tint value. In my sample set this to 0.1 (10%)

Please see also PDFlib 10 API reference chapter 1.1.4 Color Data Type for details about the correct option list syntax for colors.

I hope helps.