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)(11,14)(12,19)(13,15)(16,20)(17,23)(18,21)(22,24)(26,30)(27,33)(32,37)(34,39) involution — undirected(2,5)(6,7)(9,11,13,18)(10,14,15,21)(12,17,20,24)(16,22,19,23)(25,26)(27,31)(28,32)(29,30)(33,36)(34,38)(35,37)(39,40)(1,2)(3,6)(4,5)(7,8)(10,15)(14,21)(16,19)(22,23)(28,35)(32,37)(34,39)(38,40) involution — undirected(1,3,4,8)(2,6,5,7)(9,11)(10,14)(12,17)(13,18)(15,21)(16,22)(19,23)(20,24)(25,27,29,33)(26,31,30,36)(28,34,35,39)(32,38,37,40)(9,10)(11,14)(12,16)(13,15)(17,22)(18,21)(19,20)(23,24)(25,28,29,35)(26,32,30,37)(27,34,33,39)(31,38,36,40)(9,12,13,20)(10,16,15,19)(11,17,18,24)(14,22,21,23)(25,26)(27,31)(28,32)(29,30)(33,36)(34,38)(35,37)(39,40)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.