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