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