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