Seven different coloured books are kept one after the other.

i. The RED book is just on the top of the ORANGE book.
ii. The BLUE book is between the GREEN and the YELLOW books.
iii. The VIOLET book is between the GREEN and the BLACK books.
iv. There are as many books between the GREEN and the RED books as there are between the BLACK and the BLUE books.

If the YELLOW book is on the top, which book is exactly in the middle?