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