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