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