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