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