In the Arcueid and Ciel routes, Roa appears with long black hair in "Western" clothes.
However, I'm currently playing the Hisui route, and I've seen that the original Shiki Tohno appears in Japanese clothing with short white hair at the very end. (For what it's worth, the adopted Shiki in this route doesn't know about Roa, but the player does since she must have had to complete either the Arcueid or Ciel route first to play this route, and the information appears there.)
Yet regardless of the route, Roa and the original Shiki Tohno (which some translations name SHIKI) should be the same person. (The identity of the next reincarnation of Roa should have been decided by Ciel years before any of the different choices leading to different routes were made.) If so, why is there such a discrepancy between the appearance of Roa in the "Near Side of the Moon" routes and the Hisui route (and possibly other "Far Side of the Moon" routes)?