Hi Ram,
You can use the "area" function to color in an area under the curve. This seems like it would work well for the first region. You can use "patch" to fill in an area linearly using the vertex points or "fill" to fill in the area if you are using a function. Can you clarify what you mean when you say the points are not random and not linear? If there is an equation defining these points then you may prefer to use fill.
An example for "patch" is below for your points. Will this work?
x1 = [2.6,3,3.1,3.3,3.3,3.1,3,2.6];
y1 = [0,0,0,0,2.7,3,3.1,3.6];
x2 = x1;
y2 = [3.7,3.2,3.1,2.8,3,3.3,3.4,3.9];
figure
patch(x1,y1,'cyan')
hold on
patch(x2,y2,'blue')
