The questions asked is not related to the topic originally discussed in this thread. It is recommended to keep the forum threads on topic so that they can be helpful to others. Therefore, it is recommended to open new threads when it comes to new questions.
However, the described behavior is expected. By overriding the background-color of the DOM element representing the selected color any other selected color is not respected. At least not in the color picker. Thus, I am not quite sure what would be the need to change the decoration of the color selection from white to black, when this value should be dynamically chosen by the user and not some predefined CSS rule.
If, however, there is more behind this, I suggest you to open a new thread with more relevant information on the case.