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