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