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