One vertex per element, one color per generator, with an edge from x to x·s.
(2,4)(5,6)(7,9)(8,11)(10,12)(13,14)(15,19)(16,17)(18,20)(21,22,26,25)(23,28,24,27)(6,7)(8,12)(14,17)(15,20)(22,25)(27,28) involution — undirected(8,12)(10,11)(13,14)(15,19)(16,17)(18,20)(21,23,26,24)(22,27,25,28)(1,2)(3,4)(5,7,9,6)(8,10,12,11)(13,14)(15,19)(16,17)(18,20)(21,24,26,23)(22,28,25,27)(5,8)(6,10)(7,11)(9,12)(13,15)(14,18)(16,20)(17,19)(21,25,26,22)(23,27,24,28)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.