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)(15,19)(16,20)(17,18)(23,25)(27,28) involution — undirected(5,7)(6,9)(8,12)(10,11)(14,18)(16,19)(21,22,26,24)(23,28,25,27)(2,3)(6,8)(7,11)(13,15)(14,16)(17,20)(18,19)(21,23,26,25)(22,27,24,28)(1,3,4,2)(5,8,10,6)(7,12,11,9)(13,15)(14,16)(17,20)(18,19)(21,24,26,22)(23,27,25,28)(5,9,10,12)(6,11,8,7)(13,16)(14,15)(17,19)(18,20)(21,25,26,23)(22,27,24,28)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.