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