雲にみえるけど、実は煙だ。
It might look like clouds, but it is actually smoke.
I keep trying to answer this with みたい. Would that be a valid answer for this? If so, it would be good to add a warning and/or some extra information in brackets to make it clear. If not, why not?
雲にみえるけど、実は煙だ。
雲みたいだけど、実は煙だ。
雲雲みたいに見えるけど、実は煙だ。
Are all alright.
見える, in this case, means that you caught sight of something, and you subjectively felt it was 雲.
みたい/よう doesn’t have to be directly observed, though can be. Well, in this case, you are directly observing it anyway, but another difference is the certainty. みえる is more subjective, there is more of a guess. While みたい you had some degree of certainty based on some information, it is more objective.
みたい・ようにみえる is less certain than みたい・よう but has a nuance of directly observing it.
Well, in this case all are OK.
Thanks. Based on that I think it would be good to have a “can you try another way” message instead of marking みたい wrong.
Fixed 
@mrnoone Kind of a related question, かるそうにみえる was not accepted as an answer during my review of the grammar point even though the rule indicates it should be (いAdj[そう] + にみえる).
Is there some rule for when そうにみえる is used with いAdj with this grammar point?