Fine artists have been mixing truly beautiful colors for over a thousand years. Even though they've always been limited to the paints on hand, they learned to mix their precious pigments into an amazing variety of colors. Since black and gray pigments absorb light, artists have always avoided them. The trick was using lots of pigments, most of them in tiny amounts.
You're probably wondering what artist's colors have to do with house paint...unfortunately, almost nothing. Commercially available paint today is formulated with one strategy in mind: use as few colorants as possible, period. Since they aren't willing to add lots of colorants, they have become dependent on black and grey pigments to make colors more "natural". The question then, is how to create color that is neither garish (without black) nor dead (because black's been added).
Happily for all of us, artists have figured this out, and it's pretty darn brilliant. They use a complementary mixing system: take a little of the hue on the opposite of the color wheel (its complement), and it will soften the color naturally, without killing it. So, if I want to warm and soften a green paint, I add red. To make it even richer, I'll add yellow and blue (they make green), and then I add their complements, violet and orange.
Of course, things aren't quite that simple. The reason that paint is tricky is connected to the actual color of the pigments. When you haven't mixed paint, green colorant seems like it should be, well, just green. But the pigment has to come from somewhere, and it has the signature of that place (even if it's from a lab). How it looks and plays in a can of paint has a huge impact on the color. For instance, the 'green' colorant that's used in most paint stores is teal. That's why picking a green paint is so difficult; it's mixed from that teal/green, with some black. Since the green colorant itself is biased (towards blue) the resulting paint colors will always reflect that tendency.
There have been hundreds of customers through my shop who have chosen another paint company's color and had it turn out different that they thought it would...the wheat color is a little mustard, the tan has a mauve tone. What makes me crazy is that most people then tell themselves that they don't know color, when in fact the issue is with the paint company making limited, awkwardly biased colors. Every person knows the colors they love; the trick HAS been in picking the paint. Basically, the only way to get around the bias issue is to use a whole lot of pigments...and never black or gray. When you've got 8 to 15 pigments, the prejudice from each one is virtually eliminated.
I know this is complicated, but stay with me. It's like a recipe for pumpkin pie, if cinnamon is the only spice, the pie will taste of cinnamon. But if you add lots of spices, each adds to the flavor, and none dominate. The best part of pumpkin pie is that complex concoction of flavors.
The most amazing thing about full spectrum paint is how it changes and moves and plays with light. Because there aren't any black pigments, the shadows aren't gray. Shadows pick up on pigments that are sitting quietly, the recessive ones, if you will. So my color #73 paris™ (a gray/violet), turns cobalt or red violet or purple as the sun shifts through the day. The shadows from #39 palo verde™ (earthy yellow/green) actually break into a little rainbow, and you can see its color parents (and aunts and uncles...it has 11 pigments!)
This is probably a good place to talk about computer "color matching" services at paint stores. The matching is done with the exact program that went into creating their other colors; use two pigments and black. The only way to match a full spectrum color is using an artist's eye and an artist's mastery for color. Some think that any basic formula can become full spectrum: just remove the black and add complements. Unless there is a true complexity of pigment interaction, it is not full spectrum. A truly luminous, full spectrum color can easily take 20-40 hours of combining with a lot of wasted paint...and is breathtaking.
On a basic level, that's how full spectrum mixing works: add enough pigments to soften and enrich the color, so that it goes beyond any individual element, and becomes beautiful & real. Look at nature's colors for goodness sake. I mean really look! Get off your computer, and go look at a tree or a flower or a rock. Notice just how many colors there are in a square inch! Mama nature, the true goddess, doesn't dip lightly on her easel. She swirls & tiptoes & soars & dances & whispers & hollers with color. And she doesn't like black. So, in our own homes and offices, how can we surround ourselves with dead color? It's the largest square footage of space we've got, it creates the most feeling, and it's the cheapest interior design element you can buy (27 cents/ square foot, with two coats slathered on).
This all makes for some very time consuming mixing and expensive ingredients. There are times when I look at my formulas and think, "jeez, C J... did you HAVE to use 14 pigments?" Since I'm passionate about color & making paint easier for my customers, I get to create my own rules of paint manufacturing, and follow beauty....