One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,6)(4,5)(7,8)(9,10)(11,17)(12,16)(13,15)(14,19)(18,24)(20,22)(21,23) involution — undirected(9,11,13,19)(10,14,15,17)(12,20,21,18)(16,24,23,22)(25,26,30,34)(27,35,36,32)(28,31,38,40)(29,39,37,33)(2,5)(6,8)(25,27,30,36)(26,31,34,40)(28,29,38,37)(32,39,35,33)(1,3,4,7)(2,6,5,8)(10,15)(14,17)(16,23)(22,24)(27,36)(28,38)(31,40)(32,35)(9,12,13,21)(10,16,15,23)(11,18,19,20)(14,22,17,24)(25,28,30,38)(26,32,34,35)(27,37,36,29)(31,33,40,39)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.