It's "Shadow DIo" pretty much how he appeared in most of part 3,
I don't really know why he appeared like this since we already know what he looks like due to part 1. My guest since part 3 is Jotaro's part and we are supposedly seeing most of it from his point of view, DIo's face is blacked out due to Jotaro not knowing what DIo looks like.

As for why the artist chose to draw him like this your guest is as good as mine.