Both translations are correct. The one Duo currentl ygives talks about paper in general being white. The one you're talking about is pointing to one specific paper.
I am also of the opinion of marianpatrascuro that the question was not expressed correctly in English...
it is always a difficult task in translations :
when you have in a language one word with different meanings to get the right word in the other language where there are different expressions possible...
so you always have to do the translations backwards and forwards till you find on both sides an agreement...
in English ( as in German) you have only the word "paper" ( in German "Papier") and you can use it to say :
a paper, the paper and paper ( as a general term) ,
but in Romanian you have to make distinction between ...
o hartie ( a paper ... ein Papier)
hartia ( the paper ... das Papier)
hartie ( in general) ( paper ... Papier)
the general term is used a lot in Romanian expressions like :
hartie colorata ... colored paper
hartie de desen tehnic ... .special paper for technical drawing
hartie fotografica ... special paper for making photos
hartie cartonata ... paperboard
hartie igienica ... toilet paper
Poate aici se refera la hartie in general . In structura " The paper is white " ar face referinta la o anumita hartie , de pe birou sau mai stiu eu unde .