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