Myth Busted - Citadel colour mixing

For months now colour mixing charts are circulating on the web about a great chunk of the current Citadel range being possible to be replicated by simply mixing Skull White, Chaos Black, Blood Red, Enchanted Blue and Sunburst Yellow in the right proportions.
The story surfaced first at Nesbet Miniatures Blog and months later on the excellent Path of the Outcast Blog that I'm following. After sharing my concerns; Cannonfodder, the blog owner started a poll, asking the public what they think. 54% voted that they didn't try it but they thought it would work.
Actually it doesn't.
When I first read the original post at Nesbet's blog I shared the enthusiasm with all the rest, but after a little while things started to distub me a little.

A little on colours

For three years or so I was an active (and now honorary) member of Europa Barbarorum a project that some of you may know. It is a hardcore total realism mod for Rome (and later Medieval) Total War. Apart from skinning a few dozens of units in the mod, I was making some research into dyes and pigments, and how they work. (It was important to know what colours could be produced in the timeframe, and what was cheap or expensive.)
A colour has three major attributes: hue, saturation and lightness. It is possible to produce any colour by mixing rays of light in different colour, basically any hue can be recreated this way. What works with light doesn't work with pigments though. Pigments are of different opacity and will not produce all the hues you want. Of course I mean the pigments we modellers use; the cyan-magenta-yellow system for offset printing is an entirely different matter, and even there colours are not mixed, only dots (I know it is a bit more complex then this).
The other important thing is saturation. It is the measure how vivid the colour is. Pastel colours have more gray in them so they are of lower saturation.
The third thing to be taken into consideration is that pigments have personality... some hues you just cannot produce by mixing them. The best example is purple. In the antiquity a few grams of purple dye could feed a family for decades. Don't you think it was easier to mix or overdye madder and woad or indigo? It just did not work. Only purple dye did the job.
The charts don't, or very little address these points and this is the reason why they fail miserably.

The proof

No research is complete without experiment though, and it was relative easy - as all my readers know - I keep my citadel paints in dropper bottles. This time apart from cropping I did not use any Photoshop goodies and let the image much bigger then usual.
The results speak for themselves:

As ever, I don't pretend to have a monopoly for the truth, so if you thik that the colours are good enough proxies, or I did something wrong and you had different results, please do not hesitate to comment!
But from my part: Mith Busted.

Scout paint scheme

This week I was thinking about the best colour scheme for the scouts, these are the trial pieces:

The right one of course resembles the Sentinels' colour scheme more closely, whereas the left one for some is more pleasing. Which would you rather chose? Or perhaps a variation? lighter tan or darker grey? Please comment!

I also thinking about the chest eagle. Just have seen an excellent blood angels tutorial over All Things 40K and got totally hooked on that shoulder pad. Do you think that a chest eagle like this would look better? Please ignore the paintjob, I spent just about 5 minutes painting the whole thing.

Painting - Quest for the perfect highlights

Finding the perfect colours for the Sentinels proved rather difficult. Since there is an army to be painted I had a few principles in mind before I started to select:

1. A shade a base colour, a highlight and an extreme colour must do, there will be no more levels
2. No drybrush on the armour - on smooth surfaces I never seem to get it right...
3. Layering is preferable - Because that's the way I like it
4. No full-body washes

I had dark blue in mind, and since I'm a great fan of Regal Blue, originally chose the following colours on my trial marines:

0th variant - Original
Shade - VMC Dark Prussian Blue
Base - Regal Blue
Highlight - Enchanted Blue
Extreme highlight - 50% Regal Blue- 50% Ice Blue
I thought that it was going to be fine, but it turned out rather lame. The highlights were too crude, and I didn't like the result at all. So I went to the bits box for my leftover metal torsoes and I knew I have some serious testing to do.
Please note that I did not aim even at TTQ on the samples below, only wanted to find the most suitable colours using minimum time and effort. Here are the results

1st variant
Shade - VMC Dark Prussian Blue
Base - 50% VMC Dark Prussian Blue - 50% Regal Blue
Highlight - Regal Blue
Extreme highlight - Enchanted Blue

Actually I liked this variant, it had contrast without too extreme highlights

2nd variant
Shade - VMC Dark Prussian Blue
Base - Regal Blue
Highlight - 50% Regal Blue - 50% Enchanted Blue
Extreme highlight - Enchanted Blue

A little disappointment. While I like regal blue, this combination was a bit too low contrast.

3rd variant
Shade - VMC Dark Prussian Blue
Base - Regal Blue
Highlight - Enchanted Blue
Extreme highlight - VMC Pastel Blue

.... as this one is too much. Pastel Blue is a tad darker that the Regal Blue -Ice Blue combo I used earlier, but still too light.. At this point my wife being the one person jury chose the first variant for further improvement.

4th variant
Shade - none
Base - VMC Dark Prussian Blue
Highlight - 66% Regal Blue 33% Enchanted Blue
Extreme highlight - Enchanted Blue

5th variant
Shade - none
Base - VMC Dark Prussian Blue
Highlight - 50% Regal Blue 50% Enchanted Blue
Extreme highlight - Enchanted Blue

Since the base colour is very dark as it is, I dropped shades, and used only the highlights, which is good since it will speed up painting a bit. Perhaps I will use black liner or Badab Black ink, we shall see.
To cut a long story short Patricia and I agreed that the 4th variant looked best. Not too harsh highlights but exciting. a bit crimson fist-like look. Or Dark Angels in blue.

Do you have any tips on how could I further improve this scheme before I start painting my first tactical squad?