I’m going to refer to this previous thread as you have closed this.
This is still a problem in Pro 5.1. What I have figured out since I brought this to your attention is that the problem occurs when using a Global Color.
So if you set the ajax add to cart colours in the theme options, if you use a Global Color, then the add to cart keeps the same green as the default. If you use the colour picker without choosing a global colour then it works