As noted in the previous section, the colour layer is just that: an entire layer filled with a specific color defined by the Base Background Colour option and the Background Colour Opacity.
If you do not wish to use a background colour layer, set the Background Colour Opacity to 0. This makes the layer completely transparent, visually removing it from the composition of the image.
The transparency is there to create visually interesting effects together with an Extra Image whose layer is set to Underlay (layer 1, behind the colour which is layer 2). If you do not use an underlay Extra Image and have an opacity lower than 100% the background of your image will be semitransparent. This may be problematic, as you cannot control which background color it will be rendered on. Most sites render images over a white background, but some may do that against a darker colour.