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