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