Dear @kevin_sturm,
thank you, it works! 
But the table generated by “Color Manager” now contains 2 columns.
From the “Line Plot” help text:
The node automatically selects the column from the Color Manager and assigns the color values to the plotted columns.
…and…
Input Ports: 1: Data table containing one column with the column names of table which has in addition a color assigned. (optional)
Now that the color table has 2 columns instead of one, how does the Line Plot node know which column to take?
To answer my own question: it seems that the “Line Plot” node simply takes the first column, no matter what the name is. If the columns are moved around with the “Column Resorter” node, your solution stops working.
Maybe the help text can be made more specific?
I also would like to add that your solution does not work for the “Line Chart (JFreeChart)” node (see also this earlier post). I still often use the “Line Chart (JFreeChart)” node because it generates png images of the charts 1-2 orders of magnitude faster than the “Line Plot” node.
Thanks again and best regards,
Aswin