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