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