How can I assign custom colors to groups in a dispersion chart in Numbers?
Just called AppleCare. The guy took some time to make a chart and afterwards explained that I could click the line to change the color (just as I did before). While we were talking I clicked a dot in the graph, representing a data point. It turned out that you could change the color of the dots the same way. This color was applied to the legend, so the problem was solved.