This rainbow-colored slider allows you to quickly and easily target colors (hues) in your image. The basic workflow is:
Click on one of the color swatches at the top of the panel, which will generate a preview and make this color slider visible. The color swatch you click on sets the default hue target, as well as the center point of the color slider.
You may hold modifier keys when clicking the swatches to set a wider/narrower default range (see the tooltips). Regardless of how you start, you can aways refine the range.
You may then adjust the hue sliders to refine the range of hues which are targeted. The slider has 4 "thumbs" (the area between the center thumbs is fully selected and the adjacent areas control feathering so that the targeting of hues falls off gradually at the ends. You may click and drag the thumbs, or click in the area to move them as as a group. By default, the far left and right pairs of thumbs are locked. This gives you a default feathering and allows you to focus on the primary range of hues to target. However, you may click to move the <alt/option> clicking the sliders will split them so you may manually move the individual sliders to refine the feathering. Dragging the split sliders into each other will cause them to become locked again with default feathering.
Once you set your hue range you may further refine the preview in several ways:
Isolate to light, dark, or midtone values by clicking the D, M, L and zone buttons. You may use the regular value and precision sliders to refine this targeting.
Isolate to more or less saturated values via Sat and Vib. There are no slider controls for Sat/Vib in this context, as they are prioritized for tonal control.
Use the orange levels layer (or optional dodge/paint layers in the flyout settings) to refine the preview as desired.
Click "Not" to invert the entire preview. This works as it normally does, meaning it inverts the preview. So "not red through blue" doesn't mean simply other colors, it is the literal inverse. The intended use is to help protect a given range of colors from being adjusted. If your intent is to select other colors, just select those colors and do not use "not".