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)(11,14)(12,15)(13,16)(17,19)(18,22)(20,23)(21,24)(25,26)(27,37)(28,34)(29,35)(30,36)(31,33)(32,38)(39,40)(1,3)(2,5)(4,8)(6,7)(9,10)(11,17)(12,15)(13,16)(14,19)(18,23)(20,22)(21,24)(25,27)(26,32)(28,31)(29,39)(30,38)(33,40)(34,35)(36,37) involution — undirected(9,11,13,19)(10,14,16,17)(12,20,21,18)(15,23,24,22)(26,33)(28,39)(29,31)(32,40)(34,37)(35,36)(3,8)(5,7)(9,12,13,21)(10,15,16,24)(11,18,19,20)(14,22,17,23)(25,28)(26,34)(27,29)(30,39)(31,38)(32,33)(35,37)(36,40)(10,16)(14,17)(15,24)(22,23)(25,29,30,31)(26,35,36,33)(27,28,38,39)(32,40,37,34)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.