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