The colours for code highlighting were originally chosen to mimic the defaults in Mathematica to some extent. This was very helpful e.g. in pointing out or even just noticing mistakes in code. For example, in Mathematica blue is for undefined symbols, black is for defined ones.
Now this has been changed. The current colour scheme is has hard to distinguish colours and its colours are very confusing for someone used to Mathematica's standard.
Current colour scheme:
Mathematica's colour scheme:
What should be changed at the minimum:
undefined symbols should be clearly blue (not black, as they are now, and not dark blue that's hard to distinguish from black)
defined symbols should be black (not dark blue)
patterns should be green (not blue again)
I noticed that having colours that matched Mathematica's standards made it easier to point out mistakes to beginners. I could say things like "Notice that
BackgroundColor is blue, not black. That indicates that it is not a built-in symbol." They could see that it was blue both on the site and in Mathematica