You can use:
hasbehavior( hLine, 'legend', false );
to ensure that a given line is not picked up by the legend automatically.
In terms of the rest though it sounds more like you just want text on the plot rather than a legend.
Theoretically you could achieve this by using the above on all your actual plots and then just plot two objects out of the axis limits, one blue, one red that would appear on the legend as blue and red. It's not a nice solution though, there may be better ones.
