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