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