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