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)(16,20)(17,24)(18,27)(19,23)(21,28)(22,26) involution — undirected(5,7,8,12)(6,9,10,11)(13,15)(14,16)(17,18)(19,20)(21,27)(22,24)(23,25)(26,28)(2,4)(7,12)(9,11)(13,16,17,27,19,25,28,22)(14,20,24,18,23,15,21,26)(6,10)(9,11)(13,17,19,28)(14,21,23,24)(15,18,20,26)(16,27,25,22)(13,18,17,15,19,26,28,20)(14,22,24,16,23,27,21,25)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.