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