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