PPF on a white car: why yellowing shows first here
White and light silver are the colours where film degradation is most visible, and where cheap film gets caught.
Why white shows it
Yellowing is a slight amber shift in the film. On black it is invisible; on white it reads as a dirty panel.
What to ask
Which product line, and whether it has a UV top coat. Ask to see a white car filmed three years ago.
Prevention
Park under cover when possible, remove bird droppings quickly, and apply a coating over the film to slow contamination.
Get quotes instead of calling around. Tell us the car and the coverage — shops near you reply within a day.