Eh, that green is dark and unsaturated enough to pass as black or brown. (See how it was tagged). Reimu also has brown/reddish eyes like the girl in the picture. Well, what's the source page, anyway? If Wokada said in the tags that this is Miku with contacts I'll believe it. Anime girls are all alike anyway :P
EDIT: Source page is this: http://wokada156.tumblr.com/post/49763982589 Wokada said there that this is "Reimu-san", seemingly drawn for somebody's icon. No mention of cosplaying.