 The saturation of that colour is varied by perforating the gel sheet (or ablation of the dichroic) in a manner that permits unfiltered white light to pass through in varying amounts, progressing from full white to the fully saturated colour.At the zero DMX "start" position on a ColorFader™ scroll there is a piece of clear gel (which is perforated with large holes to maximize light transmission).As the DMX control value is increased the gel string moves to the coloured gel, which has perforated holes are that are large and plentiful - so the percentage of white light passing through those hole predominates over that of the gel colour, and low-saturation colours are achieved.