Edit a Gradient?

Get the Gradient tool (G), then click on the gradient thumbnail in the Options Bar (don’t click on the little down-facing arrow, click right on the gradient thumbnail itself). This brings up the Gradient Editor. Click on a gradient preset, at the top of the dialog, to use it as your starting point for editing (for example, if you want to create a gradient with three different colors, click on a gradient preset that looks like it has three colors [I clicked on the Blue, Yellow, Blue preset above]—it just saves you a step). Once the gradient you want to edit appears in the gradient ramp, you’ll see icons appear right below it (they look like little houses to me, but technically, they’re called color stops). You drag these color stops to the right or left to change the balance of a particular color in your gradient (you want more or less of a color), and the little diamond-shaped icon that appears between two colors controls the midpoint between them (drag one of them and you’ll instantly "get it"). To edit the color of one of these color stops, double-click on a little house icon and the Color Picker appears. To add more color stops, click directly beneath the gradient ramp. To delete a color stop, click on it and drag it away from the gradient ramp. The two opacity stops above the gradient ramp are for adding transparency. For example, if you wanted to go from black to transparent, rather than from black to a color, you would click on the opacity stop you wanted to be somewhat transparent, then choose the amount of opacity in the Opacity field near the bottom.