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