newcommand*{plotFileRainbowCertaintyLegendList}[5]{
  begin{tikzpicture}
    begin{axis}[
        %Unboxed,
        %Dates,
        %twocolumn,
        y tick label style={/pgf/number format/fixed},
        xlabel={},
        legend columns = 3,
        legend style={at={(0.5,-0.1)},anchor=north},
        #4
      ]
    %By column number
    forcsvlist{listaddLegendList}{50,52,53,56}
    %By column name
    %forcsvlist{listaddLegendList}{col1Name,col2Name,etc...}

    pgfplotstableread{#1}Mod
    pgfplotstableread{#2}ModLow
    pgfplotstableread{#3}ModHigh


    defWaveLow{360}
    defWaveHigh{660}

    pgfplotstablegetcolsof{Mod}
    pgfmathtruncatemacronumberofcols{pgfplotsretval-1}
    pgfmathsetmacro{waveStep}{(WaveHigh-WaveLow)/numberofcols}

      pgfplotsinvokeforeach{1,...,numberofcols}{
        pgfmathparse{WaveLow+##1*waveStep}
        definecolor{Offence##1}{wave}{pgfmathresult}

          addplot+[Offence##1!50,opacity=0.01,name path=confLow, mark = none, line width = 0, forget plot,#5] table [y index=##1] ModLow ;
          addplot+[Offence##1!50,opacity=0.01,name path=confHigh, mark = none, line width = 0, forget plot,#5] table [y index=##1] ModHigh ;
          addplot[Offence##1!70,opacity=0.5, forget plot,#5] fill between[of=confLow and confHigh];

        pgfplotstablegetcolumnnamebyindex{##1}of{Mod}to{colname}
        addplot+[Offence##1,solid,thick,mark=none,#5] table [y index=##1] {Mod};
        %By column number
        xifinlist{##1}{LegendList}{addlegendentryexpanded{colname};}{}
      }
        %By column name
        %xifinlist{colname}{LegendList}{addlegendentryexpanded{colname};}{}
      %}
    end{axis}
  end{tikzpicture}
}

% used PGFPlots v1.14
%
% these are just some dummy data files
begin{filecontents*}{low.txt}
x y1 y2 y3 y4 y5 y6 y7 y8 y9
1 13 23 33 43 53 63 73 83 93
9 13 23 33 43 53 63 73 83 93
end{filecontents*}
begin{filecontents*}{med.txt}
x y1 y2 y3 y4 y5 y6 y7 y8 y9
1 15 25 35 45 55 65 75 85 95
9 15 25 35 45 55 65 75 85 95
end{filecontents*}
begin{filecontents*}{high.txt}
x y1 y2 y3 y4 y5 y6 y7 y8 y9
1 18 28 38 48 58 68 78 88 98
9 18 28 38 48 58 68 78 88 98
end{filecontents*}
documentclass[border=5pt]{standalone}
usepackage{pgfplots}
    usetikzlibrary{
        pgfplots.fillbetween,
    }
begin{document}
    begin{tikzpicture}
        begin{axis}[
            no markers,
        ]
                pgfplotstableread{med.txt}Mod
                pgfplotstableread{low.txt}ModLow
                pgfplotstableread{high.txt}ModHigh

                defWaveLow{360}
                defWaveHigh{660}
            pgfplotstablegetcolsof{Mod}
            pgfmathtruncatemacronumberofcols{pgfplotsretval-1}
            pgfmathsetmacro{waveStep}{(WaveHigh-WaveLow)/numberofcols}

%            % this was the old command ...
%            pgfplotsinvokeforeach{1,...,numberofcols}{
            % ... which is replaced by a list that only contains the column
            % numbers for which the legend entry should be shown
            pgfplotsinvokeforeach{4,8}{
                    pgfmathparse{WaveLow+#1*waveStep}
                    definecolor{Offence#1}{wave}{pgfmathresult}

                addplot+ [Offence#1!50,opacity=0.01,forget plot,name path=confLow]
                    table [y index=#1] ModLow;
                addplot+ [Offence#1!50,opacity=0.01,forget plot,name path=confHigh]
                    table [y index=#1] ModHigh;
                addplot  [Offence#1!70,opacity=0.50,forget plot]
                    fill between [of=confLow and confHigh];

                    pgfplotstablegetcolumnnamebyindex{#1}of{Mod}to{colname}
                addplot+ [Offence#1,solid,thick]
                    table [y index=#1] {Mod};
                    addlegendentryexpanded{colname};
            }

            % then provide a second one the previous commands but this time only
            % with the elements that should not show up in the legend
            % (I hope you get the idea of how to do it with this example)
            pgfplotsinvokeforeach{1,...,3,5,6,...,7,numberofcols}{
                    pgfmathparse{WaveLow+#1*waveStep}
                    definecolor{Offence#1}{wave}{pgfmathresult}

                addplot+ [Offence#1!50,opacity=0.01,forget plot,name path=confLow]
                    table [y index=#1] ModLow;
                addplot+ [Offence#1!50,opacity=0.01,forget plot,name path=confHigh]
                    table [y index=#1] ModHigh;
                addplot  [Offence#1!70,opacity=0.50,forget plot]
                    fill between [of=confLow and confHigh];

                    pgfplotstablegetcolumnnamebyindex{#1}of{Mod}to{colname}
                addplot+ [Offence#1,solid,thick]
                    table [y index=#1] {Mod};
%                    % and of course this time don't provide the legend command
%                    addlegendentryexpanded{colname};
            }
        end{axis}
    end{tikzpicture}
end{document}