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