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