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