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)(15,22)(16,25)(17,19)(18,21)(20,24)(23,27)(26,28) involution — undirected(1,2)(3,4)(5,7,9,8)(6,10,12,11)(14,19)(15,23)(16,18)(20,27)(22,28)(24,26)(2,4)(14,19)(20,22)(21,25)(27,28) involution — undirected(2,4)(5,7,9,8)(6,11,12,10)(13,15)(14,20)(16,23)(17,24)(18,26)(19,22)(21,27)(25,28)(5,8,9,7)(6,11,12,10)(13,16,17,18)(14,21,19,25)(15,23,24,26)(20,27,22,28)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.