Car Paint Colour - Different Shades on Bumper / Other Metal Parts

Is it normal behaviour for some cars paint to show a different shade on different parts of the car that are plastic / fibreglass / different metal? I swear the front bumper of my Avensis (in olive green seen here) is a slightly different shade especially in some light but then other times it seems to blend perfectly depending on light / angle.

I then started noticing this on other similar colour Toyota's (mainly Avensis) where the bumper and petrol flap were slightly brighter - is this the case for Toyota and other manufacturers and their plastics used or paint or am I just seeing things? I'm almost coming to the point where I'm thinking, feck it - get it painted in case it was replaced before with the wrong colour because someone else thought it was the same in a certain light. The Avensis has so many similar silvery green colours. Cheers!