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