When something "sets the tone" it simply means that that "something" influences the ambiance/atmosphere. If you arrive at a dinner party and the hostess is wearing something very elegant and formal...that "sets the tone."
If you choose to have a wedding ceremony at the beach, that "sets the tone" - the wedding is likely to be very informal and relaxed.
It accepted "gives the tone", very literal, but I woudn't know how to write this expression in English.
It's weird to be used with vestido, it's normally with people:
Você dá o tom = you determine how it's going to be.
It's a musician's expression extended to other fields.
One musician gives the tone/note and the others follow.
Precisely. Yes sometimes the sentences are rather strange, yes sometimes you don't stand a chance to get it right first time round. But we're learning the language for free. It's not as if losing a heart is the end of the world. I'm very happy with Duolingo, and grateful to the people who do all the work to make it available
No, as emeyr wrote above "sets the tone" is an expression that means to set a point of reference, a mood, for some kind of event or situation.
I had to go through all the words with the hover hints, to come up with "sets the tone", it was the closest I could come up with.