I am creating a chart which has to use (multiple) spot colors. This color could be one that is neither accessible from RGB nor CMYK. Is there a possibility to specify a spot color for a line in matplotlib and export this to pdf? Direct export is preferred but not necessary.

Note: A spot color is a color that is not necessarily set before printing and has just a representation color until then. In the pdf it is represented as an separate color channel.

I was looking for something like this recently, I don't know if you managed to find it, but ReportLab has a method that is PCMYKColorSep.

So you could integrate the graph from matplotlib within a reportlab canvas, and add as many color separations as you see fitting.

The example above doesn't actually integrate with matplotlib, but it does add the spot

c = Canvas('test.pdf', (420, 200))
language_spot = PCMYKColorSep(0.0, 100.0, 91.0, 0.0, spotName='LanguageSpot', density=100)
c.setFillColor(language_spot)
c.rect(300, 75, 100, 100, fill=True, stroke=False)
c.save()