Interior Colour dialog box
The Interior Colour dialog box is where you select the colour to use to fill the middle area of the fractal. By default, this area is black.
To open the Interior Colour dialog box: On the Colour Palette window's Colour menu, click Interior.
The three sliders can be used to specify how much red, green, and blue is in the interior colour, allowing for over 16 million different colours. The preview box shows the colour defined by the R, G, and b sliders.