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