Two colors, one vector

I would like to plot a periodic vector, such as

x = -4*pi:0.1:4*pi;
plot(sin(x));

but to have the positive values plotted in one color and the negative values are plotted in another. Is there a simple, elegant way to do this?

Answer 1

[Azzi Abdelmalek]

x = -4*pi:0.001:4*pi;
y=sin(x);
y2=y;
y2(y2>=0)=nan;
plot(x,y ,'r',x,y2,'g');