I agree it looks completely different. But I think they're trying to appeal to a market that likes blue more than grey.
Top 3 of the NR range has undergone color changes. My guess: they didn't sell well and yonex hafta get rid of them. Unknown to me if there are any differences in performance to go along with new paint, though.
personally owned the iron grey NR900 (and broke it in a clash) and Ahsan limited edition NR900, they play the same, and only differ in paintjob. Not really sure about other NR series, but i do feel that NR900 has been underrated. It was such a solid, stiff, decently fast, and really good racket for playing doubles. 3u NR900 packs a punch and feels like most 4u rackets on yonex lineup.