One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,4)(5,6)(7,9)(8,10)(11,12)(13,14)(15,20)(16,26)(17,23)(18,24)(19,25)(21,27)(22,28) involution — undirected(5,7,8,11)(6,9,10,12)(13,15,17,25,18,21,28,26)(14,19,22,20,24,16,23,27)(6,10)(9,12)(13,15)(14,20)(16,22)(17,25)(18,21)(19,23)(24,27)(26,28) involution — undirected(2,4)(13,16,17,27,18,19,28,20)(14,21,22,26,24,15,23,25)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.