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