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