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