Conditional statements with FPLOT

How can I plot a function with regions in different colours based on if conditions using fplot?

In other words, let's say I have a function z(x) and q(x), I would like to plot z(x) in blue when condition on q(x) is satisfied, and in red otherwise. I was thinking of the following pseudocode (my functions are much more involving than sine and cosine):

z= @(x) sin(x);
y= @(x) cos(x);
if y<0 && z>0 
fplot(@(x) sin(x), 'r');
hold on
else 
fplot(@(x) sin(x), 'b');