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