Bozo,
You have just mentioned all the problems that I am facing!
bumpers and plastic parts too dark (even with the same paint!)
My new paint is too yellow also
This is what I have worked out so far
L908 P5 and R4 are all the same colour just differant internal codes for the same colour over the years
However there are according to the Glasurit site three differant tones of Gran Prix white all with the same code
One more red than the base colour and one lighter and more red
All still white of course
Not more yellow though
Weird
Graham