Yep, it turned out to be a solution in my case, although I suspect that every
can also be worked out. This is what I did. I have (it turned out) 35 blocks of floating point numbers, printed into a data file in a two column arrangement. Two blank lines are allowed between two adjacent blocks. I changed the source code minimally to also print out a 'block number" at the beginning of each block like this:
where N stands for a number: 0,1,2...
thus I knew which block I needed to use to change the color. There are many other tricks in gnuplot which I still do not understand how to use, hopefully they will come later. In principle you can almost color every point of a line with a different color if you wish but for that you have to print a separate column with the color information.