A list of values from 0.0 to 1.0 that denote fractions along the gradient.
If non-null, this list must have the same length as colors.
If the first value is not 0.0, then a stop with position 0.0 and a color equal to the first color in colors is implied.
If the last value is not 1.0, then a stop with position 1.0 and a color equal to the last color in colors is implied.
If stops is null, then a set of uniformly distributed stops is implied, with the first stop at 0.0 and the last stop at 1.0.
final List<double> stops