fill handle

[Luis Espinoza Villasante S188423]

good morning
i'm a universitarian student new to the use of octave, i need your help
because i don't know how to relate in a drawing a color with the proper
meaning of this color in a certain drawing
in other words i need that the command fill (like in matlab) allows an
handle useful to legend, like plot in the following program

 clf
 x = 0:0.1:7;
 hold on
 h(1) = plot (x, sin(x));
 h(2)=plot(x,cos(x),'r');
 h(3)=plot(x, sin(x.^2/10),'g');
 h(4)=plot(x, cos(x.^2/10),'k');
 title ("Only the sin() objects have keylabels");
 legend (h([1, 3]), {"sin(x)", "sin(x^2/10)"}, "location", "southwest");

with, instead of "plot", "fill"
indeed if i put "fill" where is "plot" i cannot see colors in legend

I thank you in advance for your precious help
see you soon!