One of the things that machine learning teaches us is that the cycle between running a test on the environment and getting feedback is critical. One of the major problems with the school system is how often the feedback loop is "take test Tuesday, teacher grades it Thursday night, student gets it back on Monday". This is useful for assessment but useless for learning.

Math is an example of where this should be used so very, very much more. Why is my first grader turning in tests covering addition when a computer can literally spit back whether it is right or wrong in a fraction of a second? The learning rate is immensely better at that speed.

And this is fantastic example of how that sort of thing could be applied to parts-of-speech learning, in real sentences rather than just an artificial "show word -> demand part of speech" test style. It's the part-of-speech equivalent of the red wavy line under misspelled words, which is also a far better way to teach spelling than any number of "spelling test Tuesday returned to student Thursday" ever could be.

It's why I like computer games.

It's why I learn programming languages way faster than real languages.

There are actually a lot of people who color code Chinese according to tones.

This is possible and is done using pinyin. The tone of the character can be highlighted in a different colour, such as CCEDICT and/or Pleco does. I have worked on this before, but the sandhi and polyphonic characters kinda complicates it a little.

I imagine people learning Latin might find it useful as well. And have a mouseover for conjugation / declension.

I made a tool that does a form of that:

http://latin.milesokeefe.com/?s=disce+quasi+semper+victurus+...

I can really see this being useful for any language.