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