The Color and Gradient Editor is a straightforward tool that can be used to adjust the coloring of various widgets.
The Solid color option allows you to manually choose a color, update RGB and Hue & Saturation, and input a specific Hex number.
The Linear Color option contains color selection options for each individual gradient point as well as options that affect the entire gradient (such as Offset, Scale, Angle and Spread).
To remove a gradient point, have that point selected and then click the X button on the right side of the gradient slider. To add a gradient point, simply hover over the gradient slider until a green button appears. Then click it to add.
The Radial Color option, just like Linear, contains individual color editable fields as well as a gradient editor. There are several Radial gradient options such as Center X, Center Y, and Radius.