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