-네 is used to express surprise or wonder.

크네: (it’s) huge!

"The cloud is very beautiful" should also be correct.

Trying to line up Korean and Japanese sentence enders is amusing, hah. 네 is like よ (and not ね), 요 adds politeness (yet hearing ㄹ까요 sounds like a mild attack if your head is in Japanese mode). What fun. :P

So there is the exclamation mark at the end of the sentence.

'clouds are really beautiful' was not accepted

the clouds sure are beautiful!