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