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