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