Let's get started.

In my first post, I mentioned that the HSV node can do some tricks and we'd "leave" that for later. Later is now.

I know some people glaze over when I give a wall of text. On the other hand, if I write as little as possible, some important lessons may be missed. So I'm going to try a balancing act. If I go too fast over something, please ask.

First topic is HSV - perhaps boring to many here. But it's important - what is Hue, Saturation, and Value? Less well known - how are these represented as numbers, and how do we do math with these? Even less well known - so what good is that - why do we care?

Hue is a property of a color that characterizes its position relative to the primary colors. Primaries are R(ed), G(reen) and B(lue). All the colors we see in computer images are made of combinations of RGB. Whenever there is a difference among R, G, and B, then the color has a hue. (If R, G, and B are the same, then the color has no hue and is a shade of gray. Everything that is not a shade of gray has a hue.)

In the attached render, I made a color wheel. Each spoke of that wheel is a different hue, and has examples of colors that all have that same hue. So going from center to outside along a spoke, we're visiting different colors but the hue is not changing. What is changing here from inside to outside is Value. Going around the circle, we're visiting different colors but the Value is not changing. What is changing going around the circle is Hue.

Value is a property of a color that characterizes its brightness. Numerically, a color's value ranges from 0 to 1. This is by definition, not by nature. The definition of 1 here means the brightest your monitor can make. There are obviously brighter colors than your monitor can make in nature - those have a value above 1. We cannot see such colors on a computer monitor. It "clips" at 1.

I have demonstrated, across the bottom, some colors that have no Hue, but clearly have a range of Values. All colors have a measurable, exact Value.

What number system goes with Hue? Different programs handle it differently. Some programs label a hue with the corresponding degrees around the circle where it appears in a color wheel. But Poser uses degrees divided by 60. (This is a historical artifact from a common way of calculating what a color's hue is that happens to assign value from 0 to 6.) We don't really care what number system is in use for Hue, as long as we understand how they work.

Why do shades of gray not have a Hue number? Because they all pile into the very center of the color wheel. They can never appear along one of the spokes, so they don't have a spoke position - therefore they have no Hue. Or, you could say they are located in every spoke, because all the spokes touch the center. Either way, you cannot name the Hue for a shade of gray.

In the 0-6 system used by Poser the Hues are anchored as shown in the render.

Red is 0 (or 6), Yellow is 1, Green is 2, and so on for Cyan, Blue, and Magenta.

For understanding leaf color manipulations, we're mostly going to care about 0, 1, and 2 (red, yellow, and green). By the strangest of coincidences, leaves change color by shifting hue from 2 towards 0!!!

Note! Hues are not confined to the integers. Colors such as orange or brown are in between red and yellow, and they have fractional hues such as .5, .737, etc. Colors between green and cyan have fractional hues between 2 and 3, such as 2.33, 2.67, etc.

When we manipulate hues, we are going to encounter and use those fractional values.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)