Hello,
I've found fill to be useful in this scenario, although it's slow, and I wouldn't recommend it if you plan to shade many many areas.
If you have the coordinates of the edges as vectors x and y (you'll start and finish at the origin I assume), then you can:
fill(x,y,C)
where C is your desired color.
I put this together real fast for the unit circle from 0 to pi/2:
x = [0 0:.01:1 0];
y = [0 sqrt(1-x(2:end-1).^2) 0];
fill(x,y,[.7 .7 .7])
axis([-1 1 -1 1])
It's colored gray and you can make it more or less detailed by changing the .01 value in the x vector.
Hope this helps!
