No. Klänning means "dress." "Clothes" is kläder, and "garment" would be klädesplagg.
That sentence is grammatically correct, but it sounds like something you'd say when referring to one out of several dresses rather than just saying that it's your dress.
No, there's no sentence with that construction. Maybe we thought it was too difficult. (and we built the course before the famous dress, so we didn't think of that one :) )
Not with colors specifically, but I believe there are some sentences later in the tree that use the "vad är det för" construction. Or at least, I learned it somewhere!
Yes, we do teach things like Vad är det för siffra? ('what figure is it') and even Vad är det för fel på dig? ('what's wrong with you') which are after all examples of the same general construction.
Wow, that is a really complicated sentence to ask what colour something is. Is there no shorter way?
The English construction is a bit illogical though, the dress 'is' not a color. Red is a color, a dress is not a color, if you see what I mean. Logic is of course very tied up to language in the first place, so I don't expect native speakers of English to agree.
But you can say Vilken färg har klänningen? 'What color does the dress have?' only that sounds a little formal.
Like 'What shape is the … earth?', if you take the first one from Google? Yes, I'd say Vilken form har jorden? in Swedish. Vad är det för form på … is also possible, but that doesn't sound great with 'jorden', it would work better with a smaller or artificial object. Anyway Vilken form är …? sounds wrong.
why is det/den always being translated with "it" and not with this/that?? I find it confusing