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