I have always use Complimentary text color for data labels in my chart as it makes the labels much easier to read. This is where I would normally go to set it:
However for unexplained reasons (the Domo Support team mentioned that this is by design) I am not able to set the same for a Line + Bar Chart type, see below where the option to select Text Color is replaced with standard color palette options.
The problem with manually setting the label text color is that it forces the same color across all the labels, so if I set it to white so it can easily be seen on the bar chart elements, the label text are no longer visible on my line chart because the white text are going against the white background.
If the complimentary option is made available, it would have been smart enough to set white text on colored background and dark text on white background. I was also told that there is no "backend enablement" for this and my only hope is to raise this here.