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