Hi fella,if you go to any paint supplies they'll mix diamond White the same way as they always do,I've never delved into asking for an exact shade of diamond White and I'd be very surprised if the program would even recognize a difference let alone the mixing guy actually get it right.really,if your painting a bonnet and a bumper I'd always recommend blending into the wings as although your car looks beautiful it will have suffered some paint fade over the years which was probably why when you saw the concours one,it most certainly would have been a different shade as fresh paint always looks different.what you could try is going to the paint suppliers yourself and stress to them what the car is and how really important it is to mix it exactly to the spec of your year of diamond White as you don't want to make it any less original than you have too,even offer to bung em a bit more for their trouble.any probs,pm me on here.