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