I think your bird was probably a Little Egret in breeding condition. The bare parts of many egrets and herons can change during the breeding season. On Little Egrets at the peak of the breeding season, the face can turn purple or blue, just for a short period during courtship (also, the feet often turn red at the same time). You mention that the bird had elongated nape feathers, which are only found on Little Egret. Swinhoe's would have a larger crest, and would usually have a yellow bill at this time of year.
Great Egret also has a bright blue/green face in breeding condition, but that would not fit your description of size or nape feathers.
