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)(27,37)(28,39)(29,35)(30,36)(31,33)(32,38)(34,40)(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)(28,31)(29,40)(30,38)(33,34)(35,39)(36,37) involution — undirected(3,8)(5,7)(9,12,14,10)(11,17,19,15)(13,16,21,20)(18,22,24,23)(26,33)(28,40)(29,31)(32,34)(35,36)(37,39)(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)(30,40)(31,38)(32,35)(33,37)(36,39)(11,19)(15,17)(18,24)(22,23)(25,29,30,31)(26,35,36,33)(27,28,38,40)(32,34,37,39)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.