“and often is his gold complexion dimm’d” which syllables should i highlight?

The syllables that Amber should highlight are of-, is, and gold. This is because only these syllables are stressed in words, meaning that the accent is there, on those words, which should be read more loudly and with more emotion that their unstressed counterparts. This poem is written in iambic pentameter, as all of Shakespeare's sonnets are, which means that the sequence of syllables goes like this: unstressed, stressed, unstressed, stressed...

So the passage is about the comic mask is ugly