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