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