The Title bar of the selected tool is orange. To collapse and subsequently expand a tool, click the triangle on the left. To change the ordering of a tool in the tool stack, drag it by its title bar.

If the Regions icon is present, it means that the tool has at least one region.

The Label contains the name of the tool by default. You can edit the label by double-clicking it to give it a descriptive name, for example “Face” or “Foreground rocks”.

The Help button opens a window that gives help for the tool.

The Enable/Disable checkbox enables or disables the effect of the tool. This includes when converting and printing.

The Delete button deletes the tool from the tool stack.

A Menu can be popped-up by control-clicking right-clicking in any blank space in the title bar. More about the menu…

If a tool is locked, a lock icon replaces the Delete button. To lock a tool, select Lock from the pop-up menu. Once locked, you can also click the lock icon to pop-up the menu.

A locked tool’s settings can not be modified. Additionally, a locked tool can not have regions added to or deleted from it, nor can they be selected or edited.

The Tool Settings tab contains various controls that affect how the tool is applied to your photo.

The Blending Mode pop-up menu allows you to select how the tool’s effect is blended with previous tools in the tool stack. More on blending modes…

The Opacity slider allows you to control how strongly the blending mode is applied to your photo. At 0%, the tool has no effect; at 100%, the tool has full effect.

The Invert mask check-box inverts the tool’s effect to be outside all of the regions of the mask for that tool rather than the default of inside. More on inverting masks…

The Color Selection tab contains various controls that allow you select the colors (and luminosities) to which the affect of the tool is applied.

You can use the Eyedropper to select a color directly from your photo.

When checked, the Enable hue checkbox restricts the tool’s effect to the selected hue range; when unchecked, all hues (for the currently selected luminosity range) are selected.

When checked, the Enable luminosity checkbox restricts the tool’s effect to the selected luminosity range; when unchecked, all luminosities (for the currently selected hue range) are selected.

The currently Selected Color is shown by the color swatch.

The Color Preset radio buttons allow you to select all red, yellow, green, blue, indigo, or violet hues directly.

The Range slider increases or decreases the range of colors selected around the color shown by the color swatch.

The Luminosity range slider controls which parts of the luminosity range are selected. The control has two sliders: one each for the lower and upper bounds of the luminosity range. Additionally, each slider splits in two that allows you to control the luminosity feathering.

More on color/luminosity selection…