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