First, you'll want the patch behind the bars, so call patch first.
You can keep the transparency on the patch, but if you don't want to blend with the bars then you'll need to make their faces fully opaque. If you want to keep the salmon-like color that you get from alpha here, you can instead 'desaturate' the color in the bar faces. I broke this out into a few lines so you can see how it works:
myshadeU(1:15) = repmat(mymax, T/2, 1);
fill = [(1:1:T)', myshadeU(1:1:T); (T:-1:1)', myshadeL(T:-1:1,1)];
patch(fill(:,1) , fill(:,2) , [0 0 1],'facealpha', 0.2);
unsaturated_hsv=saturated_hsv.*[1 .2 1];
bar(x, 'FaceColor', unsaturated_rgb); hold on