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