I am also a big supporter of the clear bra for saving the front end of the car. Have it on both of my cars and on former cars (it is on the lower part of the hood, the bumper, lights and mirrors). Never had a problem with it yellowing - but apparently this will happen if some kinds of waxes are used.
Here are photos of both of my cars. The 335 photos were taken just after Optiguard was applied in December. It went on over the clear bra as well as the rest of the car. The 135 is a sun car as it is a convertible - that car is 3.5 years old and no yellowing of the clear bra...