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