If none of the colors in the boxes satisfies your needs you can set up your own
color by moving one of the sliders for red, green, or blue with the left mouse
button. The color in the picture you want to change shows the currently
selected color and by clicking the
OK button you change your color
If the color editor has been brought up to edit the background color of the
main window three buttons labeled
Smooth are present. Activating any
of these buttons will create a color ramp for the corresponding color and mix
it with the other RGB components. The slider for this color then has no effect.
That way interesting shading effects in the background can be generated.