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