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