I agree, if you honestly want a "perfect match", take an engine part with the color you like to an auto-paint store and have them computer match you some paint. Otherwise, different batches of paint can easily vary from one batch to another. Not a perfect world... But you also need to understand that even the paint itself can be the exact same color and dry differently depending on air pressure it is shot with and how well the pigments are mixed and settled out and even the catalyst you use with the paint. Heck even the thinner added can change the color if you are not careful. That is why paint shops like to paint a small area and blend the color across the panel rather then a seam to seam body part. Blending is easier to match with feathering the paint from the patched area to the non-patched area. When you paint an entire panel, the adjacent panel(s) are can show a different hue finish.