Clicking the New or Edit button (or double-clicking a pattern) displays this dialog:
 
The large square at the left is a “FatBits” representation of the pattern; the box under it contains the pattern itself. The large square at the right contains the palette of available colors. The currently selected color is outlined (in the above example, the Black in the lower right corner is selected). Clicking in the palette selects the clicked-on color; dragging in the FatBits area changes blocks to that color.
To return to the control panel, click the Cancel or OK buttons. Cancel will discard any changes made, but OK will save the changes into the pattern list.
Reproducing Colors
Clicking on the eye-dropper icon next to the palette changes the mouse to an eye-dropper that can pick up the color of any block in the FatBits area and select that color in the palette.
Changing Sizes
Although the above example shows a 16x16 pattern, the Pattern Editor can also work with patterns 8, 16, or 32 blocks tall by 8, 16, 32, or 64 blocks wide. (A height of 64 seemed superfluous. Who has a menu bar taller than 32 pixels, anyway?) Clicking on the Pattern Size button displays the following dialog:
 
The current size of the pattern is outlined. To select a new size, click on the appropriate block, and then click the Resize button (or simply double-click the block). The FatBits area of the Pattern Editor will change shape accordingly.
Click Cancel to return to the Pattern Editor without changing the size.