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