I understand that you would like to know how to customize the appearance of the graph layout after plotting a linear regression model.
The following example fits a linear regression model and shows how you can access and modify the graphics handles returned when plotting the linear model.
>> load hald % load dataset
>> lm = fitlm(ingredients,heat)
>> h = plot(lm) % plot the linear model
>> confidenceLineHandle = h(3) % The confidence bounds line handle is the third element in the array.
>> confidenceLineHandle.Visible='off' % Hides the confidence bounds from the graph.
You can also refer to the following documentation page to learn more about "Chart Line Properties" and how to modify them. http://www.mathworks.com/help/matlab/ref/chartline-properties.html