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