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