Here's one way:
x = 1:100;
y = log(x);
xb = [1 15 55.5 100];
yb = interp1(x,y,xb);
plot(x,y)
hold on
colors = 'gyr';
for ii = 1:numel(xb)-1
idx = (x >= xb(ii)) & (x < xb(ii+1));
x_fill = [xb(ii), xb(ii), x(idx), xb(ii+1), xb(ii+1)];
y_fill = [0, yb(ii), y(idx), yb(ii+1), 0 ];
fill(x_fill,y_fill,colors(ii));
end
