I hadn't read closely the description for the exhibition
There was only one painting present by Rothko, Light Red Over Black (1957) which was shown during Rothko’s first British solo show held at Whitechapel Gallery in 1961.
The exhibition is about this particular exhibition. It displays wonderful photographs, film footage, detailed correspondences between Rothko, galleries and other artists as well as a series of recordings made by visitors to the original 1961 event.