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