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