Defining the Gradient Colors
There are several ways to set the colors through which the gradient
evolves. One is to drag and drop a few colors from the color well. This
is useful especially if you want to set a few 'key' colors of precise
RGB values.

In the color palette, below the various tabs of different color mixes,
you will find one that shows the color well. This is the one seen by
default.
You can click any of these to drag-and-drop them onto another color.
That will cause them to be exchanged. You can also drop one onto the
Primary or Secondary color.
You can also pick, drag and
drop one such color from the color well over to the gradient panel:
Drag the select color into the gradients panel, and drop it in the
scale at the bottom of the gradient.
A triangle of the same color will appearwhere you dropped it.
The gradient will now include the dropped color:
If you want that color at the very left edge, drag the triangle to the
wanted postion:
Don't move it too far, or you'll see the triangle disappear as it falls
off the edge.
Drag and drop another color from the color well, into a different place
of the gradient scale:
Now you have two control colors along the gradient. You can adjust its
horizontal position on the scale too. Move it to the right edge, for
example:
After moving the color to the right end of the gradient, drag yet
another color, near the middle:
Now we have a gradient defined by three control colors.
Here's an effect obtained by drawing a filled rectangle with this
gradient, then reversing the gradient, and drawing another, smaller
rectangle inside the first one.