This is a problem that keeps on coming up.
The funny thing about "correct" colors is most of the time the frame of reference by the vast majority of consumers is
another company's model (correct or not) or "Color Guides" printed in China from decades old color prints or slides
(or even colorized B&W prints!!!) color matched using Chinese or Japanese ink systems and printed by people who
never saw the prototype!!
Drift cards are a good start and reproducing these valuable source documents is a huge problem.
Sky / Weather Conditions
Weathering (dirt, etc. film)
Paint Fading / Deterioation
Varying Paint Formulations
Changes in Specifications over time
Scale of Color
Lower Intensity (than the Sun) Lighting Conditions on the Layout
Different Temperature Light Sources
Cumulative errors in matching colors from sub-masters
Color Perception of Individuals involved in the Research/Design/Manufacturing/Approval/Production processes
Color Perception Memory
Scale of Paint (pigment size....evident in Metalics and composites like Graphites
Paint Finish (largely not addressed in models beyond Gloss/Flat)
Sprayed paints vs. Tampo printed inks
Order of application of paints over varying color substrates
...and a high percentage of Males and even some Females have some degree of Color Blindness
Railroad Model Resources