My proposal but I cannot get it work in MATLAB 2016b
f = figure;
hax = axes(f);
[BL,BLicons] = legend(hax, 'lorem');
PatchInLegend = findobj(BLicons, 'type', 'patch');
set(PatchInLegend, 'facea', 0.5);
Syntax in Docs correspond to icons as `[lgd,icons,plots,txt] = legend(_)`.
Expected output: no box around the legend and transparency.
I have also tried unsuccessfully; which is what I have literally
[BL, BLicons] = legend( bFigHax, sprintf('Tc'), 'Box', 'off', ...
'Location', 'southwest', 'color', 'none');
MATLAB: 2016b OS: Debian 8.5