It seems there's a bit of confusion on the color wheel thing in the previous post. I had a couple of questions asking me about the relationship between chroma and value. I said that in the color wheel I presented, in each slice of the pie, the chroma changes (becomes grayer) but the value remains the same as we travel toward the center.
Sometimes our eyes are tricked into seeing lower chroma as lower (or higher) value, when they're actually the same. I really can't tell you what the scientific reason behind that is. I have noticed a tendency to confuse lighter (value) with brighter (chroma). But confusing the terminology is one thing, to actually perceive a color as lighter or darker than it is something we all experience to one degree or another.
Squinting is always a good way to simplify what you're seeing - by limiting the amount of light that the eye receives, you limit the amount of information as well, and we see only the simplified picture. If you were to squint at my color wheel, I think you can see that the values do not change within any slice of the pie.
…that is, within reason. I don't claim my pie is perfect, but the aberrations are (should be) within a few percentage points at most.
Below is a good illustration - I converted the color wheel to grayscale in Photoshop to eliminate hue information. All we see now is value. See what I mean?
I did the same with a couple of color wheels that I found online. Here's one in which the colors move toward black as it moves toward the center.
And another one in which the color moves toward white as it moves toward the center. It's got a hole in the middle, but you can see what I mean.
In all three examples, all I did was convert the color file to grayscale. There's a huge difference in what information is presented, isn't there? I really don't find the second and third color wheels helpful. I mean the second one shows what happens to a pure hue if you mix it with black, and the third one shows what happens when you mix it with white. That's not really useful information for a painter. I don't want to know what happens to red if I mix it with black or white. What I want is to be able to show how chroma affects color. I want to show that value and chroma are two different functions.
That changing the chroma of a color doesn't change its value. (Changing the value of a color does affect its chroma. Chew on that one! hint-the second and the third color wheel does show us this fact)