When using the predobs option in the plot command how do I change the line attributes of the prediction bounds

I am using a command to plot the results of a simple curve fit, ie

plot(cfTestAFTERNoOutliers,'r-',XTestAFTER,YTestAFTER,'o',outliersTestAFTER,'r*','predobs')

however the confidence intervals generated by the 'predobs' option are very thin and do not reproduce well.

How do I change the line attributes of the confidence intervals? Using 'LineWidth',2 after predobs generates an error