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