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