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