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