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