How to color some region of plot?

If I have this plot

y = [70, 72, 60, 66, 60, 57, 59, 58, 60, 73, 72, 73, 73, 72, 52, 72, 77, 59, 49, 66]; 
x = [1: 20];

what function can I use to color some region of plot, when for example y(i) > 70?

Answer 1

[Image Analyst]

Try this,using patch():

% Plot original data.
y = [70, 72, 60, 66, 60, 57, 59, 58, 60, 73, 72, 73, 73, 72, 52, 72, 77, 59, 49, 66]; 
x = [1: 20];
plot(x, y, 'b*-');
grid on;
hold on;
% Make patch of transparent color.
yl = ylim
xl = xlim
xBox = [xl(1), xl(1), xl(2), xl(2), xl(1)]
yBox = [70, yl(2), yl(2), 70, 70]
patch(xBox, yBox, 'black', 'FaceColor', 'green', 'FaceAlpha', 0.1);
hold off;

[Enrica Brunetti]

Thank you, but if I want to underline ( to color) the value of 'x', that corrisponds to the value of y(i)>70?

[Image Analyst]

Do you mean like the x values (tick labels) under the x axis??? Please post an image of what you'd like.

[Enrica Brunetti]

But if I want to color with the use of the same code, the region for y(i)< 60?

[Afiq Azaibi]

In addition to Image Analyst's solution, starting in R2023a you can use the xregion and yregion functions.

y = [70, 72, 60, 66, 60, 57, 59, 58, 60, 73, 72, 73, 73, 72, 52, 72, 77, 59, 49, 66]; 
x = [1: 20];
plot(x, y, 'b*-');
yregion(70,80,"FaceColor", 'g'); % Note, 80 is the end point so if you pan past 80, the region will stop.
yregion(45, 70, "FaceColor", 'r'); 

You can also set the EdgeColor properties to emphasize the edges but the default EdgeColor is 'none'.