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