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