Photoshop’s Gradient tool will help to enhance your project when properly utilized. In order to create a seamless gradient, you must use colors that flow smoothly from one to the other. Orange fading into green will not necessarily produce a desirable color flow, while yellow to green will usually look appealing. Using only two or three colors within a gradient will work better than trying to include everything under the sun.
Before selecting any tools, create a new layer in your file. You can find your Layer Palette under the category listed at the top titled Window. Once your palette is open, click on the Palette button and select New Layer. Label this new layer something logical and simple. Check your layer order within the layer window, making sure that your new layer is above any other layers for a clear view.
The Gradient tool is located in the toolbar on the right-hand side. It will look like a small box that is gradient going from light to dark. Select the tool and use a dragging motion while holding down your mouse across your screen. A short drag of the tool will give you a harsh gradient, quickly going from one color to another without much of a transition from one to the next. A longer drag motion using your Gradient tool will create a smoother gradient.
The dragging motion to create a gradient does not have to be contained within your image area. You may find that you need to begin the Gradient tool outside of your actual image area to achieve your goal. Make sure to do it on a separate layer in order to have control and the ability to edit. Remember that colors affect each other, including how they are viewed and the final print outcome. A shade of yellow next to blue will change how both of the colors are perceived.
—Jennifer Foy, Unisub