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