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