How can I plot a filled rectangle as a backdrop for a desired target?

I have two datasets, one of which is a target position, and the other is the actual position. I would like to plot the target with a +/- acceptable range and then overlay with the target.

I have unsuccessfully attempted the built in area, fill, and rectangle functions.

For example

    y = [1 1 1 2 1 1 3 3 1 1 1 1 1 1 1]; % Target datum
    y1 = y+1;               %variation in target size
    y2 = y-1;
    t = 1:15;
    X=[t,fliplr(t)];        %create continuous x value array for plotting
    Y=[y1,fliplr(y2)];      %create y values for out and then back
    fill(X,Y,'b');

The image produced looks like this

I would prefer it to be filled within the red boxes drawn on here