The Colour Picker
When you click either the Foreground or Background color swatch in the Tools panel or on the tool options bar,you open up the Color Picker. This dialog box allows you to select a color from the color spectrum (called a color slider) or define your color numerically.
The Swatches panel stores colors that you use often. You can add or delete colors from the panel or display different libraries of colors for different projects.
The Gradient Tool
The Gradient tool creates a gradual blend between multiple colors. You can choose from preset gradient fills or create your own.