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