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