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