Obtain opacity of primitive line

Hi all,

is there a way to obtain the alpha value of a standard primitive line after plotting?

For example:

x = 0:0.1:2*pi;
y = sin(x);
fh = figure();
ph = plot(x,y);
ph.Color(4) = 0.5; % Changes opacity
% Query color fails:
pf.Color(4) % <-- Error: Index exceeds matrix dimensions.
fh.Children.Children.Color % Results in
ans =
       0    0.4470    0.7410
fh.Children.Children.Color(4) % <-- Also fails: Index exceeds matrix dimensions.

Regards, Christian