getPhaseGradientColorMapWhiteColor() {
    const p = this._gradientMapTransitionPhase;
    const ps = p * p * (3.0 - 2.0 * p);
    const ips = 1.0 - ps;
    const fw = this._fromGradientColorMapWhiteColor;
    const tw = this._toGradientColorMapWhiteColor;
    return {
      r: fw.r * ips + tw.r * ps,
      g: fw.g * ips + tw.g * ps,
      b: fw.b * ips + tw.b * ps,
      a: fw.a * ips + tw.a * ps,
    };
  }
Gets the current Gradient Color Map white color point accounting for phase.
@return     {cc.Color}     color   The color value.