Why is colour use in academic writing disapproved?
People who are good at doing research aren't necessarily the best graphic designers. In fact most are pretty awful graphic designers. For good reason: learning to be a good graphic designer takes a lot of time and practice. So most good researchers do not have time to also become a good designers.

So if I see a researcher trying to be fancy in his design (e.g. use colors) I will automatically assume the design is going to be awful and most of the time that assumption will be correct. So I don't have a aversion to colors in academic writing per se, but it is an extremely reliable warning sign for me that some bad design is coming.

So my general advise to students is to focus on the content and keep the design as minimal as possible.