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