Normal.
Most bumper covers are painted at a different plant than where the vehicle is and at different times and different paint manufacturers.
There are some colors that have up to 10 variants to them.
A variant is when the paint manufacturer has documented a difference in the color and shading of the original paint code. You will see
lighter,darker,redder,bluer and so on depending on color and tints in that color,
and paint does act different on different materials.
In addition, flex agent added to the paint used on bumper covers are a contributing factor...