"Colorful ships are sailing on the shallow sea."
Translation:Színes hajók úsznak a sekély tengeren.
Why does it say that it's wrong when I write it exactly this way except with the verb at the end? Isn't that a common word order?
No. Well, yes. It is, but you cannot just order the words however you want, there's method to the madness. :)
The item in front of the verb stem is the focus of the sentence. In this case it's "színes hajók". We're answering the question "What is sailing on the shallow sea?" - Well, colourful ships are sailing there, this is the important part that we want to tell.
Now, there's a slightly obscure rule in Hungarian. If you have a subject in the sentence that does not have a special marker - like a, egy, sok or any number - that subject really wants to be in focus. You can't leave it unstressed, so to say.
With your word order, which I guess was "Színes hajók a sekély tengeren úsznak", you're asking the question "What are colourful ships sailing on?" to which the logical answer is "What colourful ships?" (Okay, the comparison doesn't work too well in English, but alas.) The subject is very undefined here, so it sounds odd out of focus.
I don't know what your answer was, your husband is most likely right, of course. If you notice an error in the course, please, use the "report a problem" button. There are two reasons for that: If a contributor stumbles into this discussion, they won't know what your answer was. 2. A contributor reading this might be rather unlikely, while problem reports always reach them sooner or later. :)