oops, state machine bug. It doesn't start coloring prepositions until you navigate to a different document.
And even then, because prepositionhood depends on location, I'm not smart enough to decide what is a preposition and what is a verb (li kepeken), so I just colorize all the six prepositions.
I think this is an illustration that toki pona's grammar isn't context free, which is too bad because a machine parseable toki pona would be handy for some applications.