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