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