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)(12,14)(13,20)(15,19)(17,22)(18,23)(21,24)(26,31)(27,34)(33,40)(35,36) involution — undirected(1,2,4,6)(3,5,8,7)(9,11,14,19)(10,15,12,16)(13,18,22,21)(17,23,20,24)(25,26)(27,32)(28,33)(29,34)(30,31)(35,37)(36,39)(38,40)(1,2)(3,5)(4,6)(7,8)(10,12)(15,16)(17,20)(23,24) involution — undirected(1,3)(2,5)(4,8)(6,7)(9,12,14,10)(11,16,19,15)(13,20,22,17)(18,24,21,23)(25,27,30,34)(26,32,31,29)(28,36,38,35)(33,39,40,37)(9,11)(10,16)(12,15)(13,21)(14,19)(17,23)(18,22)(20,24)(25,28,30,38)(26,33,31,40)(27,35,34,36)(29,39,32,37)(9,13)(10,17)(11,18)(12,20)(14,22)(15,23)(16,24)(19,21)(25,29,30,32)(26,34,31,27)(28,37,38,39)(33,35,40,36)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.