Normally, you draw with one solid color. Like, say, green. Gradients are a cool feature tht let you use two colors to draw with. As UltraPaint draws, it fades between the two colors in a particular way.
There are five built-in gradients, represented by
the five buttons on the main window pictured in the diagram to
the right. The white on the gradient buttons represents the left
mouse button color; the black represents the right mouse button
color. So, for example, if you choose a top-to-bottom gradient,
the left color will be on top and the right
color will be on the bottom.
You can also choose an image file as a gradient. The bright pixels in the file will represent the left color and the dark pixels will represent the right color, while colors in between will be a blend of the two. An example is displayed below: