Legend information is missing

I'm trying to plot a two y-axis graph as the following:

As you can see there is one plot missing in the legend. There should be a red square like the first one in the middle. I don't know why it is not appearing. All of the red information os the right axis. Below I show a sketch of my code:

For the fill graphs :

[ax p1 p2] = plotyy([Xaxis fliplr(Xaxis)],[Data_11' fliplr(Data_12')],[Xaxis fliplr(Xaxis)],
                                    [Data12' fliplr(Data22_2')],@(X, Y) fill(X, Y, 'c'),
                                    @(X, Y) fill(X, Y, 'r'));

For the lines:

[ax p1 p2] = plotyy([Xaxis' Xaxis'],[Curve11 Curve12],[Xaxis' Xaxis'],[Curve21 Curve22]);

As for the legend:

legend({'CI 95% - V','\overbar{V}',V','CI 95% - U','\overbar{U}',U'})

Matlab prints "Warning: Ignoring extra legend entries.".

Any thoughts?

Thanks!