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)(11,17)(12,15)(13,16)(14,19)(18,23)(20,22)(21,24) involution — undirected(2,3)(6,7)(9,10,13,16)(11,14,19,17)(12,15,20,22)(18,21,24,23)(25,26,31,30)(27,34,28,32)(29,37,38,33)(35,39,36,40)(1,2,5,3)(4,6,8,7)(12,20)(15,22)(18,24)(21,23)(25,27,31,28)(26,32,30,34)(29,35,38,36)(33,39,37,40)(1,3,5,2)(4,7,8,6)(9,11)(10,14)(12,18)(13,19)(15,21)(16,17)(20,24)(22,23)(25,28,31,27)(26,32,30,34)(29,36,38,35)(33,39,37,40)(1,4,5,8)(2,6,3,7)(9,10)(11,14)(12,15)(13,16)(17,19)(18,21)(20,22)(23,24)(25,29,31,38)(26,33,30,37)(27,35,28,36)(32,39,34,40)(9,12)(10,15)(11,18)(13,20)(14,21)(16,22)(17,23)(19,24)(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.