constructor(imageryLayer) {
    this.alpha = imageryLayer.alpha;
    this.brightness = imageryLayer.brightness;
    this.contrast = imageryLayer.contrast;
    this.hue = imageryLayer.hue;
    this.saturation = imageryLayer.saturation;
    this.gamma = imageryLayer.gamma;
    this.colorToAlpha = imageryLayer.colorToAlpha;
  }
A class containing a the values that affect the appearance of
an <code>ImageryLayer</code>.

This is used in the <code>ModelImagery</code> to detect changes in
the imagery settings: The <code>ModelImagery</code> stores one
instance per imagery layer. During the <code>update</code>
call, it checks whether any of the settings was changed.
If this is the case, the draw commands of the model are reset.

@private