Not as fine-grained as individual items of grammar, but we essentially already do this and have for almost as long as writing has been a thing. Headings in bold, things that you want to emphasise in body text in italic or bold, hyperlinks underlined and/or in a different colour, …
Highlighting by grammar might be useful in language analysers/translators, for those of us trying to learn a second, though being able to pick from a selection of rules would be needed for it to be truly useful: sometimes I might want words agreeing with each other (subject->verb, subject->adjectives) in a colour of their own, sometimes specific word types (is abierto the past participle of abrir here, or the adjective?). Or verb tenses. You could perhaps do both tense and agreement, highlighting the stem by tense and the suffix with the same colour as the subject, and object pronouns the same colour as any relevant adjectives, but this is likely to make the colouring system too complex to be useful at a glance. On anything more than a single simple sentence something more dynamic might be better here, not highlighting anything by default but when something is hovered over have it and relevant things spring into colour appropriately, you'll only need small set of colours in that case rather than one for each subject/object in a longer paragraph with trying to match the same subject/object to a set colour consistently throughout.
Here's Claud attacking your post:
