Add a new color stop (a defined color position) to the gradient defined by VectorSourceLinearGradient() or VectorSourceCircularGradient().
A gradient must at least have a color at position 0.0 and 1.0. If no colors are added for these positions then they default to solid black. Any number of color positions can be added to a gradient.
Color The 32bit RGBA color including alpha transparency. Position.d The position at which to add the color. The value must be between and including 0.0 (the gradient start) and 1.0 (the gradient end).
See VectorSourceLinearGradient() for an example.