I seem to have a similar or related issue.
I start with a jpg file having a coloured pattern (like camoflage) with just 4 colors.  There are areas of distinct colours, but there is also an overlaid pattern of letters, that betray the file as originating from shutterstock. Its not a concern to me to have that lettering, but its in a 5th color that sits on top of the others.
Thats because This exercise is just a trial of the ability to import svg into Prusa Slicer and have the pattern on the upoer layers, and see if it works.  
The file needs to convert to svg format, and one image per color.
So, I go through the process to select all the color swatches of each colour, delete(cut)  all the rest, then save the file, transfer to Pixillion, and convert the file to svg.
Rinse, Repeat for each of the 4 colors. 

The next stage of the process is to import each of the files as an embossing pattern, designed to impart different colors to areas of the 3D print, and this is accomplished by assigning each of the svg images to a different extruder, with different color filament.  Prusa Slicer 2.7 has this as a new feature.

When I import the file into Prusa Slicer, it protests, and the error message is "SVG file does NOT contain a single path to be embossed"
So, my question is, what does this error mean, and how do I cure it to make Prusa Slicer happy to import the file.

Hi. Did you ever get an answer to your question? I am having the same issue.

Thank you.