the yellowish is due to the glue of the film used.it is not the film that turns yellow.
if you look at most of the porsches, they have the film as well.
I would suggest peel it off.
not sure if autozkin is available in your country.
this definitely works better than xpel.
I've used xpel for 2 of my previous ride and let me tell you autozkin definitely beats xpel.
http://www.autozkin.com/about-us/
do check out the videos in youtube.