Jamie left out metamerism, the effect the light source can have on color perception. Alter the chemistry of the paint by using a synthetic pigment vs. a natural pigment, alter the chemistry of one of the non-pigment ingredients or substitute a safer pigment (cadmium red replaced vermillion which was mercury sulfide and cadmium is now being replaced with something else); under different light sources colors mixed to match under one spectrum of light with any of these three red pigments can shift under a different spectrum. That's why paint specs give a Munsell code (assumption is to be compared under normal daylight (5000K-5600K) and when you dig into the pigment specs they specify the light source and method to be used and the exact wavelength in angstroms the pigment should reflect (yes these specs do exist for WWII USN pigments).
As for model paint makers today the single biggest pigment problem is white. The paint base for USN colors in both world wars was white lead, there is some titanium dioxide in the paint but very little. Today we cannot use white lead. White lead paint grays out fairly quickly while titanium white does not. White lead is also not as brilliant initially as titanium white. Metamerism happens here....now what color temperature light source were you trying to compare original samples, S&S chips and Model Master paints under?
FWIW under 5000K light I found Model Master and WEM paints close enough to S&S chips and Munsell to not matter on a model with one exception. The exception is 5-D, S&S, Model Master and WEM are all far too light compared to an actual sample I found.
There can be small variances in staining power of pigments, but knowing the exact pigments used IS important because pigments don't lie. A paint made purely of white, ultramarine and black pigments will never have a greenish caste, until its linseed oil binder has been hidden in a dark folder for 20 years and adopts its own yellow hue to skew the resultant perceived colour.
Knowing the correct pigments significantly narrows the realms of possibilities. Modellers not experienced in paint mixing or conversant with real life supply chain systems will attempt mental gymnastics about all the variances that could be present, providing the theorist knows nothing of what a fixed number of given pigments mixed in different ratios are actually capable of resulting in. Paint mixers could only mix the pigments they could get. Not having a pigment they should have used due to supply is a credible argument, but suggesting they used a different pigment they shouldn't have in the military supply chain raises more questions than answers.
I liken it to Waterboarding in Guantanamo Bay. It sounds great fun, providing you don't know what either of those things are.
For some paints of course we have measured colour coordinates documented at the time following scientific measurement. Those who don't understand colour coordinates tend to dismiss these as irrelevant, in the same way that people who can't read music notation struggle to see how skilled musicians and consistently recreate the same melody from gibberish on paper. It is recognised that there were uncertainties inherent in the technology of the day, but the limits of this uncertainty still constrain the possible true colour to a fairly narrow range.
For our Royal Navy research we used all 3 in every case we could; study and measurement of extant original samples, recreation of the paints using the documented formulae, and reverse engineering of the documented colour coordinates. We compared all three to stacks of photos, film and artwork and arrived at our conclusions by consciously nailing the Light Reflectance Value targets, ensuring that the character of the hue was governed by the pigments used and original written descriptions, and the intensity of the hue was an informed judgement based on the balance of what all the above seemed to be telling us.
For example paint manufacturers have a huge say what is light gray, dark gray etc. About the only pigments on target are black and white. Model Masterís production of the S&S pigments of 5N and 50 of USN colors did not match S&S chip cards (but in the defense of Testors their 5L, 5P etc. were correct to chip card). Then if you read the paint formulations by S&S in Plastic Ship Modeler, those formulations and comments would not match their chip card.
I am thinking getting the the proper camo scheme for the time period and what was used to create that camo scheme is the important factor. Too many variables today and even for the ship painters of WW2 to say the pigment mixed was exactly what the camo designer had in mind.
Unless other wise specified paints were mixed by volume. The x parts to y parts is not dependent on units, it could be ounces, cups, quarts or gallons the ratio is the same. That doesn't mean there weren't variations due to not getting all of it out of the can or due to measuring incorrect amounts.
I remember reading that paint pigments did not come straight from a can pre-mixed . So for example 5P could 2 parts white , 1 part blue. I always wondered how much is a part? I also wonder about age of paint and was it properly mixed prior to it be mixed with another pigment? Makes a difference in shade.
Now add sun fading .....oh boy!
Hobby paint manufacturers vary in pigments. Neutral Gray in Polly Scale is not the same as Model Masters with Polly Scale being far darker.
To ease the insanity I use 5 tools. Alan Ravenís articles on ship camouflage, Navsource, Floating Drydockís two books on USN camouflage, S&S chips and this board. If a kit comes with painting instructions I usually find that they are wrong for the time frame of ship fit.
Is this all perfect.....not in the least. I have at 2 or 3 kits in my collection in wrong camo scheme that donít match timing of shipís fittings. Those are future redos
And so it goes.
Is she Gray or Blue?
This image is posted on Navsource
Here is the same image on Gettyimages