Gradients are often used when making composite images. Photoshop includes default gradient color sets and has other gradient sets listed in the drop-down menu in the Options bar.

You can also create your own gradient by sampling colorsfrom areas in your image or choosing different colors altogether.

You can add intermediate colors and design a blend among multiple colors in any order that you want. You can even design gradients that fade from any color to transparent. You can also choose a style for the gradient, such as linear, radial, angled, reflected, or diamond.

You customize the gradients from the Gradient Editor.
Start with an existing gradient and modify the colors, the color stops, and other variations in the dialog box. The possibilities are almost endless!