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