Gentleman, lets discuss some science here regarding waxes.
We all know all car paints are covered under Clear Coat. This means anything falling on car surface is actually touching the clear coat and not the car paint. With this analogy in mind, then it means that all Waxes are actually protecting the clear coat and not the car paint for that matter. So, a good wax should be able to protect all paint shades by not allowing UV rays to pass through and cause a reaction on car paint as waxes are actually protecting the clear coat and paint is hidden under neath.
And, if a Wax doesn't behave like this no matter how expensive it is, then it means that it is allowing some UV rays to pass through which is causing some UV reactions on the car paint which is less visible in dark colors but lighter colors show yellowishnes over time.
That's all folks.