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