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