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