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