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