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