To set the colour used between edges
1) On the Options menu, click Colour Palette.
2) On the Colour Palette window's Colour menu, click Edge Fill.
3) Adjust the red (R), green (G), and blue (b) sliders to the desired colour.
As you change the values, the colour between edges of open fractal windows that are showing edges changes accordingly to make it easier to see how a particular colour will look.
4) Click OK.