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