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