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