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