Colors and Patterns
The middle section of the tools window lets you select colors (using the pop-up menu or the dropper tool) and patterns. There are selectors for pattern, foreground color, background color, and transparency (for 32-bit icons).
You can also use the dropper to pick up any color you click on - a normal click sets the foreground color, and a shift-click sets the background color. If you are using one of the other drawing tools, you can quickly access the dropper by holding down the option key.
To open the standard Color Picker window, hold down the option key and click on the foreground or background color button.
The foreground color is used for the pencil, bucket, line, text, the outlines of the shapes, and the "black" parts of a pattern. The background color is used for the "white" parts of a pattern, and also as the background color when erasing, either with the eraser or the pencil. If you select something and move it (without holding down the option key), the opaque areas will be replaced by the background color. This can be useful when you want an image that doesn't have a white background, like the light gray inside the document icon.
Color Palettes
When editing the 8-bit (256-color) or 32-bit icons, there are two color palettes you can choose from: the 256-color System palette, and the standard 35 icon colors (the colors you are recommended to use in Finder icons). To switch between these, select the palette you want from the Colors menu.
The reason you may want to use the standard icon colors is that, prior to Mac OS 8.5, they are the only ones that will darken properly when an icon is selected, or that will tint properly when an item is assigned a Label color in the Finder.
As you drag the mouse across the System palette, you will sometimes see other color boxes hiliting. This is because some colors were duplicated to complete the layout; when two boxes are hilited, it's because they contain the same color.
Color Sliders
When you choose Show Color from the Window menu, you will see a set of color sliders at the bottom of the window. You can drag the sliders to set the red, green, and blue levels of the color, or switch to hue, saturation, and value mode. Click on the control above the RGB/HSV button to switch between the foreground and background color.
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