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