Umm- it's more likely to be Kokuryuu, actually. Two-kanji Japanese words usually have Chinese reading plus Chinese reading (Hakuryuu) or Japanese reading plus Japanese reading (Takahashi, say.) Kuroi is the JR for black, while ryuu is the CR for dragon. (There is a JR but I've never seen it used. People just say ryuu.) So it would make more sense to use the Chinese reading of the 'black' character rather than the Japanese one, especially since Hakuryuu uses two CRs...

if that makes any sense? I keep forgetting how complicated this language looks when you first meet it.

(Odd sidenote: oolong, the tea, (wulong in pinyin) is written with the hanzi for crow-dark and dragon. It's called black dragon tea though it has nothing to do with dragons. The wu part is the same as Ukoku's u.)