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