It's Hue! That's right, it's hue that's most important to seeing color. We tend to be more sensitive to changes in hue than to changes in brightness, and more sensitive to changes in brightness than to changes in saturation.

Imagine if traffic lights had a dark red, a medium red, and a bright red color instead of the different hues of green, yellow, and red that are commonly used. As you approached this new traffic light you might be confused wondering whether the light was medium red or dark red. However, when you approach a red/green/yellow traffic light it's easy to tell whether to go or stop.

Now let's talk about hue and saturation together.