Font Validator's output reports already have a number of "Informative" items; and users already have the options of filtering by Passed/Informative/Warnings/Errors. If it isn't an overwhelming amount of information, and is generally useful to most, it can be added with not much additional code in a fairly straight-forward manner. So do you think this is (1) of general interests , (2) does not take up too much volume or proportion of a report, to add to the output?
I have forked freetype-py (the python binding for freetype) with some additions and an example for how to use it against the diagnostics-enhanced freetype backend for FontVal. The details is in my freetype-devel posting. Mostly for people who are dead-against C# or dead-for python, I guess.
You are aware that up to 8% of Caucasian males and 1% of Caucasian females have some degree of red-green color blindness? It is one of the most widely-known and common X-linked inherited illnesses. "X-linked" as in located on the X chromosome - males has one and female two, so female can be carrier without being affected.
So one always have to be careful about relying on color to convey information - for example, if you use green-on-red for emphasis, it might have the opposite effect: a substantial part of the general population simply see it as redacted.
I am also of the opinion that legibility comes first - ornamental to the extent of sacrificing legibility isn't.