I am a former auto refinisher of 20+ years, those panels will always be a different color, simply because they are different substrates, go look at any white or pearl/metaliic color on any vehicle with plastic bumpers, they will be a slightly different shade of whatever color simply because it's the difference in plastic/smc/fiberglass vs metal ... it's annoying as hell but it's the truth. - just my 2¢ worth
Plus usually the trim pieces are painted separate of the truck.